More permissive shebang detection, highlight them

Allows for options on shebangs, like:

    #!/usr/bin/env scala -unchecked

Or -classpath or what have you. Also will match a `scalas` executable,
for the SBT script runner [1].

Refs derekwyatt#102, derekwyatt#103

[1]: http://www.scala-sbt.org/0.13/docs/Scripts.html

Author: ches

ftdetect/scala.vim

@@ -1,5 +1,5 @@
 fun! s:DetectScala()
-    if getline(1) == '#!/usr/bin/env scala'
+    if getline(1) =~# '^#!\(/usr\)\?/bin/env\s\+scalas\?'
         set filetype=scala
     endif
 endfun

syntax/scala.vim

@@ -176,13 +176,15 @@ hi link scalaSquareBracketsBrackets Type
 hi link scalaTypeOperator Keyword
 hi link scalaTypeAnnotationParameter Function
 
+syn match scalaShebang "\%^#!.*" display
 syn region scalaMultilineComment start="/\*" end="\*/" contains=scalaMultilineComment,scalaDocLinks,scalaParameterAnnotation,scalaCommentAnnotation,scalaTodo,scalaCommentCodeBlock,@scalaHtml,@Spell keepend
 syn match scalaCommentAnnotation "@[_A-Za-z0-9$]\+" contained
 syn match scalaParameterAnnotation "@param" nextgroup=scalaParamAnnotationValue skipwhite contained
 syn match scalaParamAnnotationValue /[`_A-Za-z0-9$]\+/ contained
 syn region scalaDocLinks start="\[\[" end="\]\]" contained
 syn region scalaCommentCodeBlock matchgroup=Keyword start="{{{" end="}}}" contained
 syn match scalaTodo "\vTODO|FIXME|XXX" contained
+hi link scalaShebang Comment
 hi link scalaMultilineComment Comment
 hi link scalaDocLinks Function
 hi link scalaParameterAnnotation Function