Honor $TMPDIR

[cernekee]

Some OSes, such as Android, do not have a /tmp directory. If the user sets $TMPDIR, honor that setting, otherwise default to /tmp.

For Android, TMPDIR=/data/local/tmp was tested.

@Dji75 does this help with the /tmp issue you were seeing on Cygwin (bug #295)?

[bmah888]

I'm wondering how this interacts with the "template" change that was the subject of #288 (which fixed a problem someone was having trying to port to iOS).

If we take the change in this pull request, there would then be two different ways to set the path to a temporary directory. The fact that one is in support of Android and the other is in support of iOS is not lost on me. :-)

I wonder if it's possible to make a $TMPDIR setting propagate into the tmp_template? Layering seems a bit cleaner than having two different mechanisms to accomplish similar goals.

[bmah888]

Is there still a need / desire for this functionality? If so, what about the alternate implementation I suggested in my last comment, where if $TMPDIR is defined we use that to set the already-existing tmp_template?

[bmah888]

Something along the lines of my "alternate implementation" I proposed above was done by @ralcini as as part of PR #517, although I didn't realize it until now. Somewhat belatedly closing this pull request, thanks for your submission and apologies for sitting on it for so long.