The help messages shown when argument error were redesigned and less
verbose now. When unknown or ambiguous option is given, show
suggestions like "Did you mean...". Some constant values related to
levenstein distance are borrowed from git help.c.
We replaced most of std::cerr with global::cerr. windows.h is now
included from common.h. Before including it, we define WINVER. We
renamed some variable name because some macros in windows.h collide
with them.
In MinGW32 build, global::cout is WinConsoleFile. When outputing to
console, it uses WriteConsoleW, so Unicode characters are written.
Fixed memory leak in WChar<->MultiByte conversion functions. The
portion of code which uses std::cout is rewritten to use global::cout.
Tatsuhiro Tsujikawa