[dist] update Makefile.mingw

Some make targets didn't work.
(cherry picked from commit 63038dda0205759bd66a3b606b8561e08593a259)

Conflicts:

	win32/Makefile.mingw
[bug] fix warning about alloca() with MinGW (fix #35)
(cherry picked from commit 5c27ea6ae9b0e62df00865bd6c321fc61b122378)
[bug] double free may occur

If parse_enclose() returns an error, the node '*np' will be freed in
parse_branch().  Thus there is no need to free '*np' in parse_enclose().
(cherry picked from commit 618e10ff6e777ddd91e9a362af62c93f69fcadf6)
[bug] add checking the number of capture groups (fix #24)

The number of capture groups is handled with `MemNumType` which is
`short int`. Thus the maximum number is limited to 32767.
A check of the number is added in `scan_env_add_mem_entry()`.
Also a new error code `ONIGERR_TOO_MANY_CAPTURE_GROUPS` is added.
(cherry picked from commit c7cda4ed5676167b0d01bb5555724f6164fbdb13)
[dist] remove an unnecessary include directory
(cherry picked from commit afc0c03142a16960a3f6e360933a546c308b18b3)
[dist] remove redundant rules

(cherry picked from commit 1689739c9373a2ca67664d6a088dcd624afc37fd)

Conflicts:

	win32/Makefile
[dist] create an import library

'make ptest' didn't work because the import library wasn't created.
(Actually, MinGW doesn't need an import library.)
(cherry picked from commit 4ec8a030a1e0555684075230f2c7182d3b3e922c)

Conflicts:

	win32/Makefile.mingw
[dist] update HISTORY