travis: another attempt at getting both gdal+postgis going - refs #2353
backport geojson plugin fixes from master - refs #2319 and 2367
travis: re-enable devel for proj + image libs
Merge pull request #2380 from mapnik/travis-gdal

Travis gdal
testcase for #983 against 2.3.x
fix collsion box for shields when scale_factor is used #2381
visual tests: don't exit without reporting
update expected visual images after fix for #2381
fix avoid-edges support for shields - closes #983
fix compile with boost 1.56 - refs #2368
avoid warning from boost geometry
add support for windows unicode paths in rapidxml loader
fix gdal compile with msvs 2013 - closes #2257
Bring postgis simplification factor back to 1/20 of a pixel

This was the value in 2.2.x and was accidentally changed as part
of a completely unrelated commit, see:
http://github.com/mapnik/mapnik/issues/1639#issuecomment-53388951
Merge pull request #2393 from strk/2.3.x-pgis-simplify-20th

Bring postgis simplification factor back to 1/20 of a pixel
MinGW support for SConstruct script. Build now properly detects MinGW and finds dependencies correctly.
Properly Initialize mingwbuild variable.
Added singleton unit test to check for multiple instances across multiple dynamic libraries.
Updates for supporting 64bit MinGW build on Windows 7+ via GNU tools.
Final MinGW 64 bit enhancements for Windows 7+ and Server 2008+