Document middle
merge the two versions of randmtzig_{randn,exprnd}

It seems to improve slightly (by about 5%) randn() methods working with the
global RNG, which now match the speed of those working with a (non-global)
MersenneTwister instance.
Add a note on return type in documentation of middle
check for and error early with cygwin or msys-target compilers

these are incapable of building libuv, but can build everything else
Document Cygwin-to-MinGW cross compilation

Replace old-and-busted MSYS1 instructions, no one should be using MSYS1 any more.
add a call to env in the git troubleshooting alias
set XC_HOST to `uname -m`-w64-mingw32 by default for cygwin builds
Extend call methods with rounding to Real arguments
Merge branch 'master' into rf/randn

Conflicts:
	base/random.jl
Merge branch 'rf/randn'
Fix building with USECCACHE=1.

This fixes the variable expansion and building with CMake.
Merge pull request #8906 from maleadt/pr_ccache

Fix building with USECCACHE=1.
Merge pull request #8902 from JuliaLang/tk/check-for-cygwin-compilers

RFC: Document Cygwin-to-MinGW cross compilation
Merge pull request #8916 from simonbyrne/convert-rounding2

Extend call methods with rounding to Real arguments
remove trailing whitespace introduced by #8875
Give a better trailing whitespace error message on Travis

Show offending source files with line numbers
escape space-after-colon so yaml parser stops complaining
rand() performance restored with faster code path and inlining.
Get rid of YAML parsing nit by removing colon from error message
add comment to prevent #6058 from recurring (see commit 4b4565fdd68f2fb1ab839ab409963a19201df1d4)