further gdal nodata handling improvements - refs #2023

Conflicts:
	plugins/input/gdal/gdal_featureset.cpp
tests for #2023
one more test for #2023
enable further test
fix jpeg reading regression after #1805 - closes #2123 (patch from @clundgren)
fix relative paths in mapnik-config for fonts/plugins
fix linking order in svg c++ tests
fix linux linking order in python bindings
fix boost_regex icu detection on linux when statically linking
Revert "branch 2.3.x from master at v2.2.0-242-ge85cdda"

This reverts commit 9e66317af1de3ebe8205aaefebf42514ddf82f32.
add ENABLE_SONAME option + embed rpath/loader_path by default - closes #1225
improve configure doc for FULL_LIB_PATH and ENABLE_SONAME
finish support for disabling soname on linux
scons: fix variable name
correct include for std::min/max
update a few expected test images
use premultiplied renderer for points/shields - closes #2117
another try to fix linking order on linux
boost threads are no longer needed
fix -pthread issue on linux - closes #2132