This fixes a build problem (either a type error, if doing an incremental
rebuild, or a failure to find SyntaxAra.gf if building from scratch.)
I wonder why the Travis build didn't catch this?
The -path flags in the RGL modules compiled during 'cabal build' now refer
directly to the needed source directories. References 'alltenses' and 'present'
(and the nonexistent directory 'mathematical') have been removed.
This allows the files to be compiled in any order (e.g. in parallel). In
addition, you can do things like
gf -retain lib/src/api/TrySwe.gf
without compiling/installing any other RGL modules first, and without
setting any other path flags or environment variables.
