Handle \r without a \n in cygwin

[ChrisJefferson]

This fixes the problem whereby if GAP on windows sees a \r, it will remove the next \n, no matter how far away it is.

This isn't tested, because I found it very hard to come up with a sensible test, as git (or other tools) can try to "clean up" line endings. Hopefully the PR is clean enough.

In practice, there turns out to be a whole bunch of things that could be "improved" around here, but I don't really want to rewrite lots of the file handling. This fixes a single, immediate, problem.

[coveralls]

Coverage increased (+0.0003%) to 85.076% when pulling 7e1e177 on ChrisJefferson:newlines into 1213dab on gap-system:master.

[codecov]

Codecov Report

Merging #3320 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3320      +/-   ##
==========================================
- Coverage   85.26%   85.25%   -0.01%     
==========================================
  Files         697      698       +1     
  Lines      344153   344158       +5     
==========================================
- Hits       293426   293416      -10     
- Misses      50727    50742      +15

Impacted Files	Coverage Δ
lib/process.gi	41.5% <0%> (-2.5%)	⬇️
src/iostream.c	65.39% <0%> (-0.77%)	⬇️
src/gasman.c	88.75% <0%> (-0.44%)	⬇️
src/saveload.c	67.93% <0%> (-0.28%)	⬇️
src/gvars.c	86.42% <0%> (-0.14%)	⬇️
src/vecgf2.c	75.71% <0%> (-0.12%)	⬇️
src/blister.c	98.55% <0%> (-0.04%)	⬇️
lib/morpheus.gi	84% <0%> (-0.03%)	⬇️
src/stats.c	95.13% <0%> (-0.01%)	⬇️
src/permutat.h	83.87% <0%> (ø)	⬆️
... and 13 more

[olexandr-konovalov]

I triggered a build of this PR on Jenkins here (St Andrews access only)

[wilfwilson]

@alex-konovalov What was the result of your Jenkins build? (I don't have access).

[olexandr-konovalov]

@ChrisJefferson this has to be rebased to include #3326, otherwise Windows test terminates early.