On platforms where umem is available (specifically Solaris descendents), we want
to make umem the default allocator for performance reasons and also for vtc coverage
while still keeping the malloc type as fallback option.

This reverts commit 766dee06.

Conflicts:
	bin/varnishd/mgt/mgt_main.c

varnishd sources now use cache_priv.h as primary #include, and that
includes cache.h, rather than the other way around.

In varnishtest, varnish checks now use -expect PATTERN OP NUMBER
PATTERN being a glob pattern (see fnmatch(3)).

Make all vtc checking for SMA counters stevedore-type agnostic by matching
on SM?

VDI_ functions out of $ABI VRT.

life easier for patch in the pipeline.