If you need to check for a new function or put a new target in Makefile, you
have to modify configure.in or Makefile.in.

The $(all) variable of the Makefile.in contain _all_ the files relevant to the
distribution. Please if you add a new file into this sources, add it to the
$(all) in Makefile.in, then you have just to run ./configure to update the
Makefile(s) and `config.h'.

Be warned. After modifying configure.in, Makefile.in, aclocal.m4 or
acconfig.h the best thing you can do is:

1) autoconf && autoheader
2) ./configure
3) make distclean
4) autoconf && autoheader
5) ./configure

just to be sure there is no garbage remaining in the temporary configuration
files. Better use the script `autoregen.sh'