util: check for compression engine availability before returning...
util: check for compression engine availability before returning
If a requested compression engine is registered but not available,
requesting it will now abort.
To be honest, I'm not sure if this is the appropriate mechanism
for handling optional compression engines. I won't know until
all uses of compression (bundles, wire protocol, revlogs, etc)
are using the new API and zstd (our planned optional engine)
is implemented. So this API could change.
