Take Git/usr/bin off the path on Windows

to hopefully fix starting the binaries in Cygwin or MSYS2
ref https://groups.google.com/forum/#!msg/julia-users/tCfrhMWBEwk/K4-nde_1BQAJ

adjust paths in spawn test so it still passes

contrib/windows/juliarc.jl

@@ -1,4 +1,3 @@
 # This file is a part of Julia. License is MIT: http://julialang.org/license
 
-ENV["PATH"] = JULIA_HOME*";"*joinpath(JULIA_HOME,"..","Git","bin")*";"*
-    joinpath(JULIA_HOME,"..","Git","usr","bin")*";"*ENV["PATH"]
+ENV["PATH"] = JULIA_HOME*";"*joinpath(JULIA_HOME,"..","Git","bin")*";"*ENV["PATH"]

test/spawn.jl

@@ -11,6 +11,8 @@
 #TODO:
 # - Windows:
 #   - Add a test whether coreutils are available and skip tests if not
+@windows_only oldpath = ENV["PATH"]
+@windows_only ENV["PATH"] = joinpath(JULIA_HOME,"..","Git","usr","bin")*";"*oldpath
 
 valgrind_off = ccall(:jl_running_on_valgrind,Cint,()) == 0
 
@@ -340,3 +342,5 @@ end
 
 # make sure Cmd is nestable
 @test string(Cmd(Cmd(`ls`, detach=true))) == "`ls`"
+
+@windows_only ENV["PATH"] = oldpath