Howto add additional files to GTK's build process?

["Clemens Eisserer" <linuxhippy gmail com>]

Hello,

I started playing with GTK's source a bit, however I was not able to
figure out how I can add additional source and header files to GTK.

I copied my source-files to gtk/gtk, and added the file and its header
manually to the makefile, however:
- The file is not built at all (its not in .libs)
- After running configure my makefile-changes have been overridden again

Could sombody please give me a small hint how to make the
build-process include my own files?

Thank you in advance, lg Clemens