Some jhbuild changes (past and future planned)

[Colin Walters <walters verbum org>]

Hi,

Some developers might have noticed that I've been making some changes
in jhbuild this cycle.  Why?  So I spend less time staring at other
people's build pastebins.  At a very high level, my main goals are:

* Improve the ability to do partial builds
* Try very hard to avoid "unobvious build failures"

An example of an "unobvious build failure" is stale files in the
buildroot, left over from when a module installed a file at one point,
then stopped, or moved it.  Then you might be linking to an old, no
longer built copy of a library, which can create *very* confusing
issues.   To work towards this, jhbuild now uses "make install
DESTDIR=" just like most "distributions" do, and generates a manifest
at build time.  All decent build systems (autotools, waf, distutils)
support this, so it has been mostly transparent.

I've tried to be responsive and fix problems quickly as I see them,
but some like https://bugzilla.gnome.org/show_bug.cgi?id=654592 crop
up in things I may not happen to build.  If you catch me on IRC, I
should be able to help.  Or you can file a bug.

Future changes you should be aware of:

srcdir != builddir by default
https://bugzilla.gnome.org/show_bug.cgi?id=652475

Basically, if your module doesn't support this currently, please make it do so.

parallel make
https://bugzilla.gnome.org/show_bug.cgi?id=654686

It's really not too hard to maintain if the developers active on a
project use it consistently, so just start doing it now.  (Or, add the
.NOTPARALLEL flag if you just don't care)