grep's --include option doesn't filter files passed explicitly to grep,
so when we build the file list to search in, take the filters into
account.
Also drop the --include options in this case since they aren't useful.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@5755 ea778897-0a13-0410-b9d1-a72fbfd435f5