profiles: Fix the gdk-pixbuf-loaders-cache-file hook.

'guix install' would otherwise fail with a wrong type argument whet attempting
to call the hook.

* guix/profiles.scm (gdk-pixbuf-loaders-cache-file) <file-append>: Replace
with...
<string-append>: ... this, as gdk-pixbuf has already been expanded to a string
at this point.

gnu: gtk+: Conditionally disable the tree-relationships test.

* gnu/packages/gtk.scm (gtk+)[phases] {disable-failing-tests}: Disable the
tree-relationships test on non-x86_64 targets.

gnu: uim-gtk: Build with '-O2'.

* gnu/packages/xorg.scm (uim-gtk)[arguments]: Pass "-O2 -g".

gnu: w-scan: Build with '-O2'.

* gnu/packages/video.scm (w-scan)[arguments]: Pass "-O2 -g".

gnu: transcode: Build with '-O2'.

* gnu/packages/video.scm (transcode)[arguments]: Pass "-O2 -g".

gnu: aris: Build with '-O2'.

* gnu/packages/maths.scm (aris)[arguments]: Pass "-O2 -g".

gnu: geeqie: Build with '-O2'.

* gnu/packages/image-viewers.scm (geeqie)[arguments]: Pass "-O2 -g".

gnu: gpredict: Build with '-O2'.

* gnu/packages/astronomy.scm (gpredict)[arguments]: Pass "-O2 -g".

gnu: vinagre: Build with '-O2'.

* gnu/packages/gnome.scm (vinagre)[arguments]: Pass "-O2 -g".

gnu: iftop: Build with '-O2'.

* gnu/packages/admin.scm (iftop)[arguments]: Pass "-O2 -g".

gnu: lib2geom: Skip faulty test on i686.

* gnu/packages/graphics.scm (lib2geom)[arguments]: When
'target-x86-32?', add 'skip-faulty-test' phase.

gnu: zathura: Use meson 0.59.

This fixes the build.  The problem has already been fixed on the master, but
it's not part of the latest release.

* gnu/packages/pdf.scm (zathura)[meson]: Use meson-0.59.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

build: julia-build-system: Add support for parallel tests.

The tests are defined by the script 'test/runtests.jl' from packages and the
parallelism depends on the implementation of this script.  Therefore, 'julia'
is launched using local worker processes accordingly with 'parallel?'.

* guix/build/julia-build-system.scm (check): Set the JULIA_CPU_THREADS
environment variable and invoke julia with the '--procs' option.
* guix/build-system/julia.scm (julia-build)[parallel-tests?]: New argument.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

gnu: julia: Allow parallel tests.

* gnu/packages/julia.scm (julia)[origin]<patches>: New patch.
* gnu/packages/patches/julia-allow-parallel-build.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

gnu: julia: Disable broken tests.

* gnu/packages/julia.scm (julia)[arguments]: Disable broken tests.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

gnu: glib-networking: Update to 2.70.0.

It was erroneously thought when updating to 2.70rc in commit
60e2a3bd5e1dca1b520ea16e8967fd85795fe3ef that 2.70.0 was not yet released.

* gnu/packages/gnome.scm (glib-networking): Update to 2.70.0.

gnu: libva: Update to 2.13.0

* gnu/packages/video.scm (libva): Update it.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

gnu: Remove python2-itsdangerous.

* gnu/packages/python-xyz.scm (python2-itsdangerous): Delete variable.

gnu: python2-pylibmc: Remove package.

* gnu/packages/databases.scm (python2-pylibmc): Delete variable.

Signed-off-by: Ricardo Wurmus <rekado@elephly.net>

gnu: python2-validators: Remove package.

* gnu/packages/python-xyz.scm (python2-validators): Delete variable.