Fix tarball and install, particularly for INSTALL

Getting the INSTALL file generated from the markdown, into the tarball
via CPack and not otherwise installed is a bit tricky. I did this
manually for 5.0, but this automates things. CPack source archives use
a mechanism that acts on whole directories. So we put INSTALL into its
own output directory (as we do for generated HTML), and the
directory-globbing mechanism takes care of it fine. Added some
documentation for why we need to do this.

Added more CPack-time checks that the tarball will be complete.

Prevented installation of .gitattributes.

Change-Id: I77c645faf7b292a085165bdd1598741dae6972a5
Make selections ignore \r in input

Now the selection engine treats \r (as well as various other space
characters) the same as a space.  Added a unit test for this.
There is an extra trailing space in some cases that may be more common
with \r\n than otherwise, but that is a separate, mostly cosmetic
issue.

Fixes #1555

Change-Id: I78dfe8e477133b98a98fecf1fad243262f9b30c8
Make IEEE754 check more robust

This change should prevent compilers from
optimizing away the structure used for checking
strings in the binary by also using it to produce
a return values. There are now also clearer
warnings, and if IEEE754 cannot be detected we
fall by to using the OS versions of erf/erfc()
in double precision. Fixes compiles on Power7.

Change-Id: I8ed834d5b87baf33e03725d2ab93a60a76c34a12
Fix Cygwin build

Doesn't work with AVX but I suspect this to be Cygwin's/GCC's fault.

GCC Bug 61730

Change-Id: I171e8414a8d65800804226034604a9973770bfdd
Merge release-5-0 into master

Conflicts:
	cmake/gmxCFlags.cmake (adjacent changes)

Change-Id: I45088d7b5256613971b9926fc5fa50511a2ed743