try-files: add a server block for testing
request: don't optimize in response to our loopback fetches
system-test: test RetainComment
housekeeping: we updated the binaries, so we don't need to keep these copies
Merge pull request #214 from pagespeed/jefftk-try-files-loopback

Don't try to optimize loopback fetches
Merge pull request #215 from pagespeed/jefftk-retain-comment

system-test: test RetainComment
system-test: PreserveURLs
system-test: check that we respect no-transform
Merge pull request #217 from pagespeed/jefftk-respect-no-transform

system-test: check that we respect no-transform
Merge pull request #219 from pagespeed/jefftk-remove-duplicate-files

we updated the binaries, so we don't need to keep these copies
system-test: check rewriting images works
system-test: check jpeg and webp rewriting quality
system-test: check that we respect the Vary: User-Agent
Merge pull request #221 from pagespeed/jefftk-respect-vary

system-test: check that we respect the Vary: User-Agent header
system-test: shard domain

* Test ShardDomain
* Improve error message when options cannot be set at location scope
** Used to say `"pagespeed" directive Option cannot be set at location
   scope`, now says `"pagespeed" directive "ShardDomain" cannot be set
   at location scope`.
* Marked `CustomFetchHeader`, `MapOriginDomain`, `MapProxyDomain,
  `MapRewriteDomain`, and `ShardDomain` as legal to set in location
  blocks.  In `mod_instaweb.cc` they're listed under `All two parameter
  options that are allowed in <Directory> blocks`.
Merge pull request #223 from pagespeed/jefftk-test-domain-sharding

system-test: shard domain
system-test: check LoadFromFile works
Merge pull request #225 from pagespeed/jefftk-test-load-from-file

system-test: check LoadFromFile works
caching-headers: respect 'ModifyCachingHeaders off'
Merge pull request #227 from pagespeed/jefftk-dont-modify-caching-headers

caching-headers: respect 'ModifyCachingHeaders off'