building on t2 in 4 hours

[John H Palmieri]

I just built Sage on t2.math.washington.edu in four hours, with only
one cheat:

- The cheat: I used an installation of atlas from a previous Sage
build.

This saves 10-12 hours. With this cheat, I have in the past been able
to build Sage in 17 hours. To cut it down to 4 hours: install the
patches at #8306 (parallel inter/intra-spkg building). The result
(after fixing one small mistake in SAGE_ROOT/spkg/standard/deps):

real 243m24.846s
user 833m14.300s
sys 129m48.406s

...

Sage build/upgrade complete!

(The "real" line is the key one. Since it was building parallel, the
"user" time is longer than the actual elapsed time.)

I'm happy to give #8306 a positive review, but it depends on some
other tickets -- #8731, #9185, #9186, and #9187 -- so please review
those. Several of them involve very small changes to spkg-install
files, but someone more familiar than I am with makefiles and related
issues should review them.

--
John