develop branch and m4 version on cascade

[edoapra]

m4 version 1.4.13 on cascade does not work
modified travis/install-autotools.sh t get 1.4.16
M4_VERSION_MIN=1.4.16

[edoapra]

I have just realized that this issue has been already been mentione by Ajay in
#33 (comment)

[jeffdaily]

No worries. I've been working on a fix for it this week in addition to other build issues to go out as a v5.6.1 release. Changes are currently in hotfix/5.6.1 branch. See
https://github.com/GlobalArrays/ga/compare/hotfix/5.6.1
for current changes.

[abhinavvishnu]

Edo -- can you please do a quick code review?

[edoapra]

Sure. hotfix/5.6.1 correctly builds the needed version of m4 on cascade