Reviewed by Mark Rowe.

        Various JavaScript string optimizations
        https://bugs.webkit.org/show_bug.cgi?id=39051

        Approximately 1% SunSpider speedup.
        
        * runtime/ArrayPrototype.cpp:
        (JSC::arrayProtoFuncJoin): Remove branches from the hot code path
        by moving the first pass outside the loop, and duplicating the hot loop
        to extract the loop-invariant branch.
        * runtime/RegExp.cpp:
        (JSC::RegExp::match): resize ovector to 0 instead of clearing to avoid
        thrash in case of large matches.
        * runtime/RegExpConstructor.h:
        (JSC::RegExpConstructor::performMatch): Mark ALWAYS_INLINE to make the
        compiler respect our authority.
        * runtime/StringPrototype.cpp:
        (JSC::jsSpliceSubstringsWithSeparators): Inline.
        (JSC::stringProtoFuncSubstring): Rewrite boundary condition checks to
        reduce the number of floating point comparisons and branches.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@59355 268f45cc-cd09-0410-ab3c-d52691b4dbfc