Prevent gzip files from being gratuitously different.

By default, mtime is 0 and in that case, Zlib will set it to Time.now,
and each time the same uncompressed file is compressed, the output will
be different. So I chose another integer, 1 seemed nice, but any would
do, it just needs to be the same every time.
Engines#engines apidoc fix
Fix MultiJson api
Use the asset's mtime instead of a constant.
Merge pull request #321 from Absolight/fix-gzip-mtime

Prevent gzip files from being gratuitously different.
Update changelog for 2.4.1
Sprockets 2.4.1
Fix processing mixin docs
Only try args as a path if its a string
Merge pull request #318 from steel/master

Don't break manifest.compile if a regex is passed in.
Fix multijson feature detect
Merge pull request #324 from ixti/doc-fixes

Fix processing mixin docs
Update changelog for 2.4.2
Sprockets 2.4.2
Include dependency paths when calculating mtime
Fix Time rounding issue in tests for 1.8.7
Merge pull request #325 from petebrowne/dependency-paths-mtime

Include dependency paths when calculating mtime
Expose sprockets context to sass
Add changelog entries for 2.4.3
Sprockets 2.4.3