mx env file processing

[Tom Rodriguez]

I made a minor change to the processing of env files that shouldn’t impact most people.  Previously mx.mx/env happened to function as a global env file that was read by all suites but this was really an unintended behavior.  There is now an optional per user ~/.mx/env file that can hold global options and mx.mx/env is only read when it is the primary suite.  https://ol-bitbucket.us.oracle.com/projects/G/repos/mx/browse/README.md <https://ol-bitbucket.us.oracle.com/projects/G/repos/mx/browse/README.md> explains the env file loading process in more detail.

tom