Merge branch 'sk/mingw-uni-fix-more'

Most of these are battle-tested in msysgit and are needed to
complete what has been merged to 'master' already.

* sk/mingw-uni-fix-more:
  Win32: enable color output in Windows cmd.exe
  Win32: patch Windows environment on startup
  Win32: keep the environment sorted
  Win32: use low-level memory allocation during initialization
  Win32: reduce environment array reallocations
  Win32: don't copy the environment twice when spawning child processes
  Win32: factor out environment block creation
  Win32: unify environment function names
  Win32: unify environment case-sensitivity
  Win32: fix environment memory leaks
  Win32: Unicode environment (incoming)
  Win32: Unicode environment (outgoing)
  Revert "Windows: teach getenv to do a case-sensitive search"
  tests: do not pass iso8859-1 encoded parameter

compat/mingw.h

@@ -210,6 +210,9 @@ char *mingw_getcwd(char *pointer, int len);
 
 char *mingw_getenv(const char *name);
 #define getenv mingw_getenv
+int mingw_putenv(const char *namevalue);
+#define putenv mingw_putenv
+#define unsetenv mingw_putenv
 
 int mingw_gethostname(char *host, int namelen);
 #define gethostname mingw_gethostname
@@ -357,12 +360,8 @@ int mingw_offset_1st_component(const char *path);
 void mingw_open_html(const char *path);
 #define open_html mingw_open_html
 
-/*
- * helpers
- */
-
-char **make_augmented_environ(const char *const *vars);
-void free_environ(char **env);
+void mingw_mark_as_git_dir(const char *dir);
+#define mark_as_git_dir mingw_mark_as_git_dir
 
 /**
  * Converts UTF-8 encoded string to UTF-16LE.