[SPARK-9001] Fixing errors in javadocs that lead to failed build/sbt doc

These are minor corrections in the documentation of several classes that are preventing:

```bash
build/sbt publish-local
```

I believe this might be an issue associated with running JDK8 as ankurdave does not appear to have this issue in JDK7.

Author: Joseph Gonzalez <joseph.e.gonzalez@gmail.com>

Closes #7354 from jegonzal/FixingJavadocErrors and squashes the following commits:

6664b7e [Joseph Gonzalez] making requested changes
2e16d89 [Joseph Gonzalez] Fixing errors in javadocs that prevents build/sbt publish-local from completing.

4 files changed, 11 insertions, 7 deletions

diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSet.java b/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSet.java
index 28e23da108..7c124173b0 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSet.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSet.java
@@ -90,7 +90,7 @@ public final class BitSet {
    * To iterate over the true bits in a BitSet, use the following loop:
    * <pre>
    * <code>
-   *  for (long i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i + 1)) {
+   *  for (long i = bs.nextSetBit(0); i &gt;= 0; i = bs.nextSetBit(i + 1)) {
    *    // operate on index i here
    *  }
    * </code>
diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSetMethods.java b/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSetMethods.java
index 0987191c1c..27462c7fa5 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSetMethods.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/bitset/BitSetMethods.java
@@ -87,7 +87,7 @@ public final class BitSetMethods {
    * To iterate over the true bits in a BitSet, use the following loop:
    * <pre>
    * <code>
-   *  for (long i = bs.nextSetBit(0, sizeInWords); i >= 0; i = bs.nextSetBit(i + 1, sizeInWords)) {
+   *  for (long i = bs.nextSetBit(0, sizeInWords); i &gt;= 0; i = bs.nextSetBit(i + 1, sizeInWords)) {
    *    // operate on index i here
    *  }
    * </code>
diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java b/unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
index 8d8c08de52..d0bde69cc1 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
@@ -404,14 +404,17 @@ public final class BytesToBytesMap {
      * at the value address.
      * <p>
      * It is only valid to call this method immediately after calling `lookup()` using the same key.
+     * </p>
      * <p>
      * The key and value must be word-aligned (that is, their sizes must multiples of 8).
+     * </p>
      * <p>
      * After calling this method, calls to `get[Key|Value]Address()` and `get[Key|Value]Length`
      * will return information on the data stored by this `putNewKey` call.
+     * </p>
      * <p>
      * As an example usage, here's the proper way to store a new key:
-     * <p>
+     * </p>
      * <pre>
      *   Location loc = map.lookup(keyBaseObject, keyBaseOffset, keyLengthInBytes);
      *   if (!loc.isDefined()) {
@@ -420,6 +423,7 @@ public final class BytesToBytesMap {
      * </pre>
      * <p>
      * Unspecified behavior if the key is not defined.
+     * </p>
      */
     public void putNewKey(
         Object keyBaseObject,
diff --git a/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index 60d050b0a0..e7f9fbb2bc 100644
--- a/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -330,8 +330,8 @@ public final class UTF8String implements Comparable<UTF8String>, Serializable {
   /**
    * Returns str, right-padded with pad to a length of len
    * For example:
-   *   ('hi', 5, '??') => 'hi???'
-   *   ('hi', 1, '??') => 'h'
+   *   ('hi', 5, '??') =&gt; 'hi???'
+   *   ('hi', 1, '??') =&gt; 'h'
    */
   public UTF8String rpad(int len, UTF8String pad) {
     int spaces = len - this.numChars(); // number of char need to pad
@@ -363,8 +363,8 @@ public final class UTF8String implements Comparable<UTF8String>, Serializable {
   /**
    * Returns str, left-padded with pad to a length of len.
    * For example:
-   *   ('hi', 5, '??') => '???hi'
-   *   ('hi', 1, '??') => 'h'
+   *   ('hi', 5, '??') =&gt; '???hi'
+   *   ('hi', 1, '??') =&gt; 'h'
    */
   public UTF8String lpad(int len, UTF8String pad) {
     int spaces = len - this.numChars(); // number of char need to pad