Make -e/-E options conditional on HAVE_REGCOMP in help text
Add -I option to specify include regexes
Add implementation for -I option
Remove accept_path check for watched directories

Prior to this change, directories are first checked with accept_path()
before being watched, when using the File System Events monitor. This
means that with an --include regex of '\.c$' (for example), only
directories with a '.c' extension will be watched. This is probably not
intended. Rather, only the files that change should be checked with
accept_path().
Refactor code for include / exclude regexes