Validate paths during DirCheckout

Validate paths during DirCheckout

DirCacheCheckout and CanonicalTreeParser cooperate. CanonicalTreeParser
can detect malformed, potentially malicious tree entries and sets a
flag, while DirCacheCheckout refuses to work with such paths.

Malicious tree entries are ".", "..", ".git" (case insensitive), any
name containing '/' and (on Windows '\') and also (on Windows)
any paths ending in a combination of '.' or space or containing a ':'.
We also forbid all special names like "con" etc on Windows.

Some of the test can execute on any platform by enabling partial
platform emulation.

A new runtime exception, InvalidPathException, is introduced. For
backwards compatibility it extends InvalidArgumentException.

Change-Id: I86199105814b63d4340e5de0e471d0da6b579ead
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>