Incorrectly generated reconfigure rule in case when agcat was run with -C option

[ethouris]

In case when agcat was run with -C <directory>, the reconfigure rule is still generated with -f Makefile.ag option, while it is actually not valid. Tracking the source directory and the Silverball file should be done as both and to stay universal, both -C and -f options should be used in the generated reconfigure rule.