[minor] clean up dependencies in make clean, and exclude them from git

.gitignore

@@ -8,3 +8,5 @@ doc/*.html
 *.a
 *.so
 *.o
+src/*
+!src/mig

Makefile

@@ -101,6 +101,7 @@ clean:
 	rm -f libmig_gpgme.a
 	rm -rf bin
 	rm -rf tmp
+	find src/ -maxdepth 1 -mindepth 1 ! -name mig -exec rm -rf {} \;
 
 clean-all: clean
 	rm -rf pkg