[bugfix,dunecontrol] Fixes sed statements to capture sequences variables.

Some ^[$BLANK] or [^[$BLANK]^'], where $BLANK is space followed by tab
did not work as a capturing statement in some cases (e.g. opts files
with CONFIGURE_FLAGS="CXX='bla'"). After this patch we use [$NOBLANK]
with NOBLANK=^$space^$tab which works. In addition the other patches
form feature/posix-sed-dunecontrol have been backported to close flyspray
1401.