extension filter in "find in files" dialogue

Hi
   Quite often I'm writing code that uses c and cpp files, and I would like to be searching across al c, cpp h, etc files.  I'm forever having to select a combined filter from the drop down list in which I added *.c to the standard c++ search filters.
  It seems every time you switch to a different file the filter selection box changes back to the default for that files extension. I can understand why but still frustrating. Could an option be placed somewhere to stop this behaviour? or is there a place somewhere where these default search filters can be changed?
I've changed the langs.xml files to give all of the extensions (c h hpp hxx cpp cxx cc) to both the c and cpp types, and this seems to have fixed the filter issue, but is this the correct thing to do?? Because now every time I load a c file into the editor it ends up setting the language options to c++ ( which I can kind of live with), though if I leave the file in there and change the language for the c file to c from the list and then close and reopen np++ it seems to magically remember that I changed it to c...
  Could we perhaps add another entry into the xml for each file extension to specify a filter list for each known file type?? eg another optional xml entry..
This would really help for finding across multiple extensions, other examples might be php html and xml searching.. there are elements of an overall webpgae spread across all those extensions and you want to search across them all to find something..

Cheers
   Richard