Rebuild after ./mach test-unit

(ugly) workaround for issue #3928
Moved unit tests to the end of `./mach test`
glutin - Add support for waking up blocked event loop, and smooth resize on mac.
auto merge of #4048 : mttr/servo/mach_unit_test_fix, r=larsbergstrom

This is a quick and dirty workaround for issue #3928. Basically, `cargo test` is deleting `./target/servo`, which is clearly not ideal if we want to do anything with servo after running the unit tests. This PR makes sure to rebuild after running `./mach test-unit`.

I'm not familiar enough with cargo yet to know why it's doing this or what better alternatives there are to fixing this. Having to rebuild afterwards feels pretty ugly to me, but my rationalization right now is that the time it takes to build is negligible in comparison to the time it takes to run the tests. Ideally, this should be something we could take care of in Cargo.toml, but again, I'm new to this (and the documentation seems less than helpful from what I can tell so far).

I won't be available for the rest of the day, so if anyone has suggestions, or wants to wait for a better solution, I'll get back to it tomorrow probably. Otherwise, this PR at least makes `./mach test` work properly, so there's that.
auto merge of #4442 : glennw/servo/glutin-events-resize, r=larsbergstrom,larsbergstrom
Use event polling instead of blocking when outputting to a file.

This stops some ref tests on linux blocking while waiting for
user input events and never outputting the file.

Also mark vertical writing test as flaky on all platforms. Due
to unrelated timing reasons, this fails reliably on mac when glutin
is enabled. The related bug with details on the root cause is #3926.
gfx: Refactor the border drawing code and split out fragment display
list building into multiple functions.

This should have no functional changes; it's just code cleanup.
gfx: Fix a nasty bug whereby the transient clip was not always removed,
causing elements to be randomly clipped out.

Improves Wikipedia, Reddit, etc.
gfx: Clip the background properly when `border-radius` is used.

Improves Reddit, GitHub, etc.
auto merge of #4459 : pcwalton/servo/border-radius-clipping, r=glennw

Together these improve a large number of sites: GitHub, Reddit, Wikipedia, etc.

r? @glennw
Update glutin to get mac visibility fix.
auto merge of #4461 : glennw/servo/glutin-tests, r=larsbergstrom

This stops some ref tests on linux blocking while waiting for
user input events and never outputting the file.

Also mark vertical writing test as flaky on all platforms. Due
to unrelated timing reasons, this fails reliably on mac when glutin
is enabled. The related bug with details on the root cause is #3926.