Fix expected values of setup tests on Windows

Fix expected values of setup tests on Windows

On Windows, bash stores absolute path names in shell variables in POSIX
format that begins with a slash, rather than in drive-letter format; such
a value is converted to the latter format when it is passed to a non-MSYS
program such as git.

When an expected test value is constructed, it must contain the value that
will be produced by git, which will be in the drive-letter format. But
TRASH_DIRECTORY is in POSIX format. Fix this by using $(pwd), which
produces drive-letter format since 4114156a (Tests on Windows: $(pwd) must
return Windows-style paths).

The change in t1510 is a straight seach-and-replace, except for the first
hunk of the diff.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>