\jmescope affects global state instead of environment

The \jmescope[n] command, which is a hack to give \var and \simplify a JME scope to work with, is now a standalone macro which affects global state instead of taking a TeX argument.
It looks like it works, but I'm worried about race conditions, so I'm going to ask the MathJax people about it.
better \var and \simplify without \jmescope

thanks to Davide Cervone of MathJax.
Merge branch 'master' into stable