SI-9833 Fix -nobootcp in the Unix scala script

This was not having the desired effect of placing the
Scala library on the JVM's regular classpath.

This commit honours this setting.

Note that the Windows scripts have never supported
the use of bootclasspath, so no changes are required.

The existing bug:

```
(java_use 1.8; ~/scala/2.11.8/bin/scala -nobootcp -debug -e 'print("")')

/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/bin/java
-Xmx256M
-Xms32M
-Xbootclasspath/a:/Users/jason/scala/2.11.8/lib/akka-actor_2.11-2.3.10.jar:/Users/jason/scala/2.11.8/lib/config-1.2.1.jar:/Users/jason/scala/2.11.8/lib/jline-2.12.1.jar:/Users/jason/scala/2.11.8/lib/scala-actors-2.11.0.jar:/Users/jason/scala/2.11.8/lib/scala-actors-migration_2.11-1.1.0.jar:/Users/jason/scala/2.11.8/lib/scala-compiler.jar:/Users/jason/scala/2.11.8/lib/scala-continuations-library_2.11-1.0.2.jar:/Users/jason/scala/2.11.8/lib/scala-continuations-plugin_2.11.8-1.0.2.jar:/Users/jason/scala/2.11.8/lib/scala-library.jar:/Users/jason/scala/2.11.8/lib/scala-parser-combinators_2.11-1.0.4.jar:/Users/jason/scala/2.11.8/lib/scala-reflect.jar:/Users/jason/scala/2.11.8/lib/scala-swing_2.11-1.0.2.jar:/Users/jason/scala/2.11.8/lib/scala-xml_2.11-1.0.4.jar:/Users/jason/scala/2.11.8/lib/scalap-2.11.8.jar
-classpath
""
-Dscala.home=/Users/jason/scala/2.11.8
-Dscala.usejavacp=true
-Denv.emacs=
scala.tools.nsc.MainGenericRunner

print("")
```

Fixed by this patch:

```
⚡ (java_use 1.8; qscala -nobootcp -debug -e 'print("")')

/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/bin/java
-Xmx256M
-Xms32M
-classpath
/Users/jason/code/scala/build/quick/classes/repl-jline-embedded:/Users/jason/code/scala/build/quick/classes/repl-jline:/Users/jason/code/scala/build/quick/classes/repl:/Users/jason/code/scala/build/quick/classes/compiler:/Users/jason/code/scala/build/quick/classes/library:/Users/jason/code/scala/build/quick/classes/reflect:/Users/jason/code/scala/build/quick/classes/interactive:/Users/jason/.ivy2/cache/org.apache.ant/ant/jars/ant-1.9.4.jar:/Users/jason/.ivy2/cache/org.apache.ant/ant-launcher/jars/ant-launcher-1.9.4.jar:/Users/jason/.ivy2/cache/org.scala-lang.modules/scala-asm/bundles/scala-asm-5.1.0-scala-1.jar:/Users/jason/.ivy2/cache/org.scala-lang.modules/scala-xml_2.12.0-RC1/bundles/scala-xml_2.12.0-RC1-1.0.5.jar:/Users/jason/.ivy2/cache/jline/jline/jars/jline-2.14.1.jar
-Dscala.home=/Users/jason/code/scala/build/quick
-Dscala.usejavacp=true
-Denv.emacs=
scala.tools.nsc.MainGenericRunner
-nc

print("")
```

1 files changed, 3 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/ant/templates/tool-unix.tmpl b/src/compiler/scala/tools/ant/templates/tool-unix.tmpl
index 5e6b3c041e..7ab23eb556 100755
--- a/src/compiler/scala/tools/ant/templates/tool-unix.tmpl
+++ b/src/compiler/scala/tools/ant/templates/tool-unix.tmpl
@@ -160,7 +160,7 @@ while [[ $# -gt 0 ]]; do
       shift 2
       ;;
     -nobootcp)
-      unset usebootcp
+      usebootcp="false"
       shift
       ;;
     -usebootcp)
@@ -189,14 +189,13 @@ declare -a classpath_args
 
 # default to the boot classpath for speed, except on cygwin/mingw/msys because
 # JLine on Windows requires a custom DLL to be loaded.
-unset usebootcp
-if [[ -z "$cygwin$mingw$msys" ]]; then
+if [[ "$usebootcp" != "false" && -z "$cygwin$mingw$msys" ]]; then
   usebootcp="true"
 fi
 
 # If using the boot classpath, also pass an empty classpath
 # to java to suppress "." from materializing.
-if [[ -n $usebootcp ]]; then
+if [[ "$usebootcp" == "true" ]]; then
   classpath_args=("-Xbootclasspath/a:$TOOL_CLASSPATH" -classpath "\"\"")
 else
   classpath_args=(-classpath "$TOOL_CLASSPATH")