[Qgis-developer] Running QGIS from build directory

[Martin Dobias]

Hi devs

finally I got this done: ability to run QGIS directly from the
directory where you build it. No need to run 'make install' everytime
as it was necessary before. Now it is possible to run/debug QGIS from
your favourite IDE without having to add additional install steps
and/or set custom run command. It's in git master.

Some notes to the solution:
The built executables, libraries and modules are now created in
"output" subdir within your build directory. The rest of the files
(svg, resources etc) are accessed from the source tree. In order to
find out whether qgis is installed or not we look for source_path.txt
file in the path where qgis binary is created. CMake creates this file
with path to source tree. This way QGIS is able to set the paths
properly. There are few new methods in QgsApplication that tell
whether QGIS runs from build directory and what paths are used for
source tree and build output.

I have tested on linux only so far. It should not affect the
functionality when installed. There are few things I am aware of that
do not work right now when run from build directory (though they work
when installed):
- python plugins included in source tree (fTools, installer, gdal
tools, osm) are not visible. Their source files would need to be
copied to some directory so that they see the generated files -
otherwise they would fail to start
- help viewer does not open help files

Comments are welcome.

Martin