[PATCH] Honor the SOURCE_DATE_EPOCH variable Implement the SOURCE_DATE_EPOCH specification[1] for reproducible builds. If SOURCE_DATE_EPOCH is set, use it as timestamp instead of the current time.
[PATCH] testsuite: use SOURCE_DATE_EPOCH Instead of the special --invariant flag, use SOURCE_DATE_EPOCH (and the volume-id option) for reproducible build. (Plan for eventual removal of the --invariant flag.)
Use "export SOURCE_DATE_EPOCH=1426325213; command" instead of the simpler "SOURCE_DATE_EPOCH=1426325213 command". Both forms work in bash, but apparently only the "export" version works in dash. Run in a subshell to not leak SOURCE_DATE_EPOCH.
