Replace rak::regex with fnmatch from POSIX <fnmatch.h>

rak::regex was a hand-rolled glob matcher supporting only '*'
wildcards. Replace it with the standard POSIX fnmatch() which supports
the same glob patterns plus '?' and '[...]' character classes.

- src/core/manager.cc: use fnmatch for directory entry filtering
- src/command_download.cc: use fnmatch for file path pattern matching
- Makefile.am: remove rak/regex.h from EXTRA_DIST
- rak/regex.h: deleted, no longer needed

Makefile.am

@@ -7,7 +7,6 @@ nobase_dist_pkgdata_DATA = \
 	lua/rtorrent.lua
 
 EXTRA_DIST= \
-	rak/regex.h \
 	scripts/checks.m4 \
 	scripts/common.m4 \
 	scripts/attributes.m4