"debug_invalidate_system_caches_always" is too long

As I've been poking around in this area, I find myself growing
increasingly annoyed at the new GUC name
"debug_invalidate_system_caches_always". It is too d*mn long.
It's a serious pain to type in any context where you don't have
autocomplete to help you. I've kept referring to this type of
testing as CLOBBER_CACHE_ALWAYS testing, even though that name is
now obsolete, just because it's so much shorter. I think we need
to reconsider this name while we still can.

I do agree with the "debug_" prefix given that it's now visible to
users. However, it doesn't seem that hard to save some space in
the rest of the name. The word "system" is adding nothing of value,
and the word "always" seems rather confusing --- if it does
something "always", why is there more than one level? So a simple
proposal is to rename it to "debug_invalidate_caches".

However, I think we should also give serious consideration to
"debug_clobber_cache" or "debug_clobber_cache_always" for continuity
with past practice (though it still feels like "always" is a good
word to lose now). "debug_clobber_caches" is another reasonable
variant.

Thoughts?

regards, tom lane