In order to support use of roaring bitmaps in the loader, we need to
depend on it here.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

The dependency cache in LoadElement causes the peak RAM consumption of
the loader to be exceedingly large, upwards of 25GB for a test of a
Debian stack.  By switching from the old dict cache to a roaring bitmap
based cache, we reduce the cost of the loader cache in RAM terms to
around 5.5GB for the same stack, which makes it plausible for the short
term.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

Switch to roaring bitmaps for the loader dependency caches

See merge request !1128

The unix specification for unix sockets only allocates ~100 characters
for the length of the path. This may be longer than the path for a CI
runner, or the path to a user's buildstream directory.

Add pre-merge tests that use a WSL runner

Closes #852

See merge request !1108

Daniel Silverstone authored Feb 06, 2019 and Benjamin Schubert committed Feb 06, 2019

The licence for roaringbitmap was not compatible.  pyroaring is
a similar project which is MIT licensed and is slightly better on
memory too.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

loadelement.py: Switch from roaringbitmap to pyroaring

Closes #899

See merge request !1133

The 'wallclock-us' is a option that we thought we already had.