Fixes running 'hg serve' with Windows executable and no explicit template path configured. PY2EXE executables don't support __file__ but do place the directory of the shared code library into sys.prefix. Fixes bug 152.

adding foo
adding bomb
adding a.c
adding dir/a.o
adding dir/b.o
! a.c
! dir/a.o
! dir/b.o
? .hgignore
a.c: unsupported file type (type is fifo)
! a.c