fix(file_list): Incorrect response after remove and add file

Remove and then immediately add same file can lead to
incorrect content in response. Because pending timeout after remove
may resolve early then file will be processed, and in response get not
processed content.
docs(config): updates for clarity and consistency
docs(about): updates for clarity and consistency
fix(proxy): More useful proxyError log message

Update the log message to output the 'message' attribute of the Error so
that more is logged than merely "[object Object]".
docs(troubleshooting): add the common ws issue
fix(config): #1113 Watching is not working properly on linux

Solve bug in watch service by using pooling

Closes #1113
chore(merge_pr): compare to upstream/master

Also fixes some old comments to canary instead of stable.
chore(merge_pr): handle canary behind master

Before, if canary was behind master, a PR would always get merged into canary.
Merge branch 'pr-1045' into presubmit-master-pr-1045
Merge branch 'pr-1100' into presubmit-master-pr-1100
chore: release v0.12.19
Merge branch 'pr-1055' into presubmit-master-pr-1055
fix(preprocessor): treat *.swf files as binary
fix(preprocessor): treat *.gz files as binary
Merge branch 'pr-1114' into presubmit-master-pr-1114
chore: release v0.12.20
fix(web-server): cache static files

Files in `karma/static/*` were always read from file system.
These files typically don’t change (except when developing Karma itself)
and so it makes sense to cache them in memory.
Especially `./static/context.html`, which is read for every test run.

The main reason for this change is that when using native events
(non-polling), watching can easily hit the EMFILE limit and then this
`fs.readFile()` can be super delayed. This was easily reproducible
problem in AngularJS test suite.
chore: release v0.12.21
fix(preprocessor): treat *.tgz, *.tbz2, *.txz & *.xz as binary

Tarballs often use extensions joined with used compression, e.g. *.tgz instead
of *.tar.bz.

Also, there is a new xz lossless compression format that is slower but gives
better results than gzip or bzip2.
docs(readme): svg badges