BUG: fix handling of infs in hypot on windows

On any platform where we used our own implementation of hypot, (e.g.
windows) there were several issues with infs.

hypot(inf, y) == inf, for all y including nan.  We now check for inf and
handle this case explicitly for all y instead of just y = nan.

Although hypot(inf, 0) was correctly returning inf, it was incorrectly
raising the invalid floating point exception.

Fixes gh-2385
Merge pull request #3992 from ewmoore/winhypot

BUG: hypot(inf, 0) shouldn't raise a warning
DOC: add 1.7.2 release notes
Merge pull request #3997 from juliantaylor/release-notes

DOC: add 1.7.2 release notes
MAINT: Don't use 'import *' in lib/test_twodim_base.py.
ENH: lib: Rewrite vander: make it faster, and add an option to specify the order of the powers (either decreasing or increasing).
MAINT: lib: remove unused imports and PEP8 clean up in twodim_base.py
MAINT: lib: Add a 'See Also' section to the vander docstring, and make a few more PEP8 tweaks.
MAINT: lib: Use a consistent PEP8-compliant import style in twodim_base.py and tests/test_twodim_base.py.  Also make a couple more PEP8 tweaks.
Merge pull request #3999 from WarrenWeckesser/vander

ENH: lib: Rewrite vander
DOC: update 1.7.2 release notes

add two additional fixed bugs
Merge pull request #4003 from juliantaylor/release-notes

DOC: update 1.7.2 release notes
DOC: fix layout of issue listings in release notes
Merge pull request #4004 from juliantaylor/doc-updates

DOC: fix layout of issue listings in release notes