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.
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
rename Uint => UInt (closes #8905)
Merge pull request #8907 from JuliaLang/sk/UInt

rename Uint => UInt (closes #8905)
fix slow hash(::SubString{<:ByteString})

Cuts the #8826 vocab.jl benchmark in half.
make Travis fail if trailing ws is detected
remove trailing ws from repo
Merge pull request #8914 from JuliaLang/jcb/rmtrailingws

Remove all trailing whitespace (again)
remove ws from a couple of files in docs/
Extend call methods with rounding to Real arguments
fix jl_static_show formatting for long long printing (ref #8402)
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