Update .gitignore for config.cache.

Also add a comment about why regreesion.* aren't listed in .gitignore.

Jim Nasby

.gitignore

@@ -28,6 +28,7 @@ lib*.pc
 
 # Local excludes in root directory
 /GNUmakefile
+/config.cache
 /config.log
 /config.status
 /pgsql.sln

src/test/regress/.gitignore

@@ -5,3 +5,7 @@
 /tmp_check/
 /results/
 /log/
+
+# Note: regreesion.* are only left behind on a failure; that's why they're not ignored
+#/regression.diffs
+#/regression.out