t800[12]: work around MSys limitation

MSys works very hard to convert Unix-style paths into DOS-style ones.
*Very* hard.

So hard, indeed, that

	git blame -L/hello/,/green/

is translated into something like

	git blame -LC:/msysgit/hello/,C:/msysgit/green/

As seen in msys_p2w in src\msys\msys\rt\src\winsup\cygwin\path.cc, line
3204ff:

	case '-':
	  //
	  // here we check for POSIX paths as attributes to a POSIX switch.
	  //
	...

seemingly absolute POSIX paths in single-letter options get expanded by
msys.dll unless they contain '=' or ';'.

So a quick and very dirty fix is to use '-L/;*evil/'. (Using an equal sign
works only when it is before a comma, so in the above example, /=*green/
would still be converted to a DOS-style path.)

Commit-message-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>