[mk/sysdep] Fix sqlite3-tcl sysdep on Gentoo

Gentoo installs the package under lib/sqlite-3.7.7.1/, so let robotpkg search
in lib/sqlite-3* in addition to the usual path (lib/sqlite3).

While here, add SYSTEM_PKG.Gentoo (although this won't be used ATM, because
mk/platform/opsys.sh is lacking proper support for this distribution).
[mk] Recognize Gentoo distributions in $OPSYS

Gentoo does not have a /etc/lsb-release file, so add a quirck in
platform/opsys.sh, testing for /etc/gentoo-release. The version reported
by this file and filled in $OS_VERSION is the version of the
sys-apps/baselayout package.
[mk/platform] Teach robotpkg about Gentoo and OpenNao
[mk/sysdep] Add some SYSTEM_PKG names for Gentoo sysdeps
[mk] Fix internal log filter in case of killed process

Make sure the variable holding the exit code of the filtered command is not
empty. This happened once when the command was killed by linux (by OOM?).
[hardware/cwiid] Add missing dependency on gtk
[graphics/rcpdf-interface] Add missing dependency on doxygen
[middleware/omniORBpy] Default to a 'robotpkg' package on Gentoo and similar

Portage does not seem to have a package for omniORBpy.
[math/jrl-mathtools] Fix configure on Gentoo

Workaround a name clash with variable PKG_CONFIG_VERSION.
See patch-ab for details and
https://github.com/jrl-umi3218/jrl-cmakemodules/issues/25
[devel/boost-libs] Fix SYSTEM_SEARCH.boost-libs on Gentoo

Boost library names may contain a version tag, e.g. libboost_regex-1.48.so

This how boost is installed Gentoo, and this commit fixes the SYSTEM_SEARCH for
all boost libraries on this platform.
[interafces/jrl-mal] Fix configure on Gentoo

Workaround a name clash with variable PKG_CONFIG_VERSION.
See patch-aa for details and
https://github.com/jrl-umi3218/jrl-cmakemodules/issues/25
[math/jrl-mathtools] Fix configure on Gentoo

Explicitly pass BLAS_LIBRARIES and LAPACK_LIBRARIES as found by robotpkg to
cmake. Also add a dependency on blas. This is needed because:

1. blas and BLAS_LIBRARIES is required on Getoo because FinBLAS.cmake is
   patched on this platform to use pkg-config. However, this breaks the
   semantics of various BLAS_* variables normally defined by the regular
   FindBLAS.cmake. Explicitly passing BLAS_LIBRARIES is sufficient in
   math/jrl-mathtools to workaround this issue, as this is the only variable
   used (indirectly by FindLAPACK).

2. Passing LAPACK_LIBRARIES is also required because of an issue with
   cmake-2.8.6. This is a different way to work around the broken
   FindLAPACK.cmake (typos) with cmake-2.8.6, and replaces the previous quirk
   consisting in distributing a FindLAPACK in ${FILESDIR}.
[interfaces/jrl-mal] Update blas and lapack variables passed to cmake

It seems that passing BLAS_LIBRARIES and LAPACK_LIBRARIES to cmake (instead of
BLAS_blas_LIBRARY and LAPACK_lapack_LIBRARY) also works for overriding cmake's
idea of blas and lacack.

In addition, this fixes some issues on Gentoo and/or with cmake-2.8.6 which
have a broken FindBLAS.cmake and FindLAPACK.cmake, respectively. See commit
9b1a367 for details.
[image/opencv] Update depend.mk for opencv>=2

The depend.mk already checks for opencv>=2.2.0, but the SYSTEM_SEARCH was still
referring to opencv1 files. Recent opencv have dropped these files, so update
SYSTEM_SEARCH.
[image/opencv] By default, use system's OpenCV
[middleware/omniORBpy] Fix depend.mk for the debian sysdep

debian omniORBpy is split into several packages, account for this in
SYSTME_PKG.Debian. Also add mandatory files in the SYSTEM_SEARCH.

At runtime, the package also needs a special PYTHONPATH in omniidl_be, so
export that too.
[image/sift] Add missing INSTALLATION_DIRS
[mk/sysdep] Add SYSTEM_PKG.Gentoo for gtk+

While here, add a <3 version constraint, since the SYSTEM_SEARCH is tuned for
gtk+-2 only.
[mk/sysdep] Drop useless license boilerplate of gtk sysdep
[image/opencv] Fix depend.mk for PREFER.opencv = system

Commit f67e0cc was wrong: old opencv headers are still installed by modern
opencv. This is just the debian package that is split in a weird manner and
both libopencv-dev and libcv-dev must be installed. Both are needed since most
of the packages using opencv never bothered with updating their includes path
to opencv2.

So re-add include/opencv in the SYSTEM_SEARCH, and while here mention the
SYSTEM_PKG names for supported platforms.