Merge pull request #131 from dariomanesku/master

Unused local variable problem fixed.
Updated mouse wheel message.
Mouse wheel fix.
Mouse wheel fix.
Fixed GCC warning.
Manually integrated some FreeBSD changes from @lye #132 pull request.
Merge branch 'master' of github.com:bkaradzic/bgfx
Manually integrated some FreeBSD changes from @lye #132 pull request.
FreeBSD ifdefs.
Fixed NaCl debug build.
Fixed Issue #128 caused by read from unaligned memory (undefined behavior? when running asmjs).
Using imguiCollapse instead of imguiButton for imguiColorWheel.
Fixed drawText() to handle NULL or empty string.
Added imguiImageSwizzle().
Added imguiBorderButton().
Added imguiTabs().
Added optional _height param for imguiSeparator() and imguiSeparatorLine().
Fixing imgui scroll area scissoring.
Function setWindowTitle() now returns void.
Making setWindowTitle() on Windows thread safe.