prelim vpa support
minor cleanup
backslash with vpa raises warning

b/c its not consistent with double for over determined systems
Merge branch 'backslash' into vpa
fix typo
use sympy's "N" to make Floats

allows `vpa('pi')` to work.
vpa quieter tests
add vpasolve

wip
Merge remote-tracking branch 'origin/master' into vpa

Conflicts:
	NEWS
some xtests leave things in a messy state, work around
Merge pull request #157 from cbm755/vpa

VPA support