changed: run test for a x different than pi

this to workaround roundoff differences occuring near sin(pi) on
different compilers/hardware
Merge pull request #44 from akva2/fix_roundoff_issue_in_syntax_test

changed: run test for a x different than pi
Minimal fix for Eigen versions lacking pow(Eigen::Array).
Merge pull request #46 from atgeirr/fix-lackofpow

Alternative fix for Eigen versions lacking pow(Eigen::Array).