koji: exit early if spec has uncommitted changes

When running 'make koji', the tooling will attempt to create a new git
tag with a name constructed from the spec file's NVR.

However, if there are uncommitted changes to the Name, Version, or
Release fields (collectively, NVR) in that file, the new tag's name will
not match the NVR in the spec file referenced by commit HEAD.

Protect against the mismatch by exiting early from a 'make koji' if any
spec file modifications are not yet committed to the repo, and alert the
user what the problem is.

Signed-off-by: Patrick McCarty <patrick.mccarty@intel.com>

Makefile.common

@@ -293,6 +293,10 @@ koji: prekoji-checks kojidef
 		echo "Error: Must be on the master branch to submit to koji" >&2; \
 		exit 1; \
 	fi; \
+	if ! git diff --quiet HEAD ${SPECFILE}; then \
+		echo "Error: All changes to ${SPECFILE} must be committed first" >&2; \
+		exit 1; \
+	fi; \
 	if git rev-parse --verify --quiet origin/master > /dev/null; then \
 		git pull --rebase; \
 	fi