Export user variables before their definition

[TomekTrzeciak]

It would be useful to have user environment variables exported as soon as they are defined, so they could be used in further definitions like so:

FOO='foo'
BAR=$(script_using_FOO)

instead of:

FOO='foo'
BAR=$(export FOO; script_using_FOO)

This pull request moves the export of variables before their definition, which makes them exported as soon as they are defined.

[TomekTrzeciak]

There are currently two tests failing - tests/env-filter/00-filter.t and tests/jobscript/00-torture.t . Both of them rely on the current structure of the jobscript, so this is expected, but before changing anything in tests I'll wait for the feedback on this pull request.

[hjoliver]

@TomekTrzeciak - at first glance, this seems a good idea, thanks. There seems to be a lot of spurious commits on your branch; perhaps you need to rebase it onto master?

[TomekTrzeciak]

Sorry, I've botched my local branch and then pushed that to github. The spurious commits should be gone now and the tests should be updated as well.

[hjoliver]

Looks good; tests as working.

[matthewrmshin]

(Change is harmless and is an improvement to the intention of the current functionality. My normal comment (e.g. metomi/rose#1221) applies when it comes to the motivation of the use case, however.)

[oliver-sanders]

Existing tests provide adequate testing for this change.