This can be used like --conditions=+doc,-wayland in order to modify the
condition set from the commandline.

The user's jhbuildrc is capable of inspecting conditions set from the
commandline by way of checking

    if 'flag' in conditions:
        ...

but the arguments on the commandline always override what is written in
jhbuildrc.  This is done by applying the modifiers twice -- once before
parsing the config and then again, after.

https://bugzilla.gnome.org/show_bug.cgi?id=720839

JHBuild isn't just for GNOME 1.x and 2.x, but 3.x too and other software

The formerly autotools modtypes expect this.

These both were previously pointing at nonexistent directories and
doing random internals hackery to make the build succeed.

This was pretty much pointless - we aren't testing waf's behavior
at that point.

It would be more useful to add a real waf module, like we have for
e.g. 'hello'.  But this would imply checking waf into jhbuild git,
which...eh.

Some of the tests were of type AutogenModule, but just pointing to
/tmp.  This kind of worked before for a few reasons (we weren't
checking the error code, the old install machinery didn't use DESTDIR
and check contents).  Even worse the tests would change behavior if
you happened to have a Makefile in /tmp.

Since some of these tests are just testing behavior of the
buildscript, create a MockModule type that explicitly doesn't do
anything.

At the same time, for other tests, ensure we're actually looking at a
nonexistent directory.

Duplicate packagedbs are bad.

We had two copies of the same test.

This supports more of the basic framework, and thus helps more of
the tests pass.

Based upon patch by Adam Dingle

As we are now (1dda018a) using the waf script
shipped with modules.

libhello was looking for libtool data files in jhbuild toplevel directory
which can't work since the toplevel configure.in doesn't call AC_LIBTOOl.
Let libhello configure.in know that it should look in its own dir for libtool
data files by calling AC_CONFIG_AUX_DIR(.)