Fix a race condition in btrace.  Flush the log file before unlocking it.

 * This same exact race condition existed in the exec-interposing version
   of btrace, but I reintroduced it during the rewrite.
MurmurHash3: Fix a build error on FreeBSD 9.1 with g++47.

 * On FreeBSD 9.1 with the g++47 compiler, the compiler complains that a
   call to an always_inline function in fPIC mode, with -O2, is not inlined
   because it can be overwritten at link-time.

 * I am skeptical of the continued use of always_inline.  I think it could
   be removed, but I don't see the point in doing so.  If upstream ever
   fixes the build error, they should consider using "static inline" and
   nothing else.
Allow the cwd to be NULL.

 * This comes up when indexing the FreeBSD kernel.  When it happens, put
   an empty cwd string into the log file.  I'm not sure *why* it's
   happening.  Maybe the directory was deleted?
Make the tab stop size configurable at run-time.

 * The setting is configurable via new menu items:
       View
           Tab Width
               [ ] Tab Width: 1
               [ ] Tab Width: 2
               [ ] Tab Width: 3
               [ ] Tab Width: 4
               [ ] Tab Width: 5
               [ ] Tab Width: 6
               [ ] Tab Width: 7
               [ ] Tab Width: 8
Fix an inaccuracy in SourceWidgetView::sizeHint.

 * The code was not updated during the switch from integral to
   floating-point font coordinates.  It still used an integral character
   width, so the width of the viewport could be too narrow to show all of a
   line.