Added a types.h with vim.h unsigned int typedefs.
Extract file_search.c from misc2.c

Continue to split misc2.c in many other files (see #209).

The only changed I made to the moved code was adding
`vim_free(ff_expand_buffer)` to `free_finfile()`. This is was needed
because `ff_expand_buffer` was moved from `misc2.c` to `file_search.c`.
test: add C free() definition

Interning won't work without it.
test/misc2: add tests for strsave family

Incomplete but at least it shows a test written in plain lua.