fixup attempt on .travis.yml

try to store error codes by putting $? inline using ;
tweak .travis.yml

exporting inline captures the error code, but apparently removes
it from the pipeline, so we should exit using that code right after
fixup gdb lines in .travis.yml

they should use -q and run in batch mode
wrap exit commands when used in .travis.yml
Don't link SDL_gpu in plain SDL builds.
avoid scanning all units for a unit filter which gives a location

This adds a specialized implementation of unit filter -- if unit
filter specifies numbers for both x and y (no , - and not "recall")
then to find all matches we just find that position in the unit_map
rather than scan over all units. This happens behind the scenes.
Merge branch 'master' of git://github.com/wesnoth/wesnoth
remove debugging output from travis
Query dimensions from screen_ instead of screen.
Fix preproc directive.
revert 82932815423db27df4574665b7caf1e61c912292, fix segfault again
Use the SDL_OPENGLBLIT flag only for SDL_gpu builds.
Fix VC build for 5d3040c0b
Fix a few typos in comments & debug output
Merge pull request #235 from aquileia/VC_update

tiny VC update, typo fixes
try to fix some travis wierdness

by putting time statement outside of the multiline if statement
add -g run_wml_tests option to run gdb backtrace in case of crash

And use it on travis
cleanup .travis.yml

- Don't install gdb twice
- Time the gdb install
- If the cpp tests return any code >= 128 then apply gdb
- Add some comments
fix a typo in travis.yml
precompute a unit_filter outside of a loop