Use uri_has_scheme to find out if the href in Webdav responses is absolute
to use the matching base path extraction.
Signed-off-by: Vincent Petry <PVince81@yahoo.fr>

No need to copy it to a buffer.

The ones in std have overloads for const char/char.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Reduce overhead by not duplicating the string.

Required according to RFC 3986:

> An implementation should accept uppercase letters as equivalent to
> lowercase in scheme names

Closes #330

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

New in clang 3.6.

A file called ".jpg" is not a JPEG file with an empty name; it is
merely a hidden file.

Replaces g_uri_parse_scheme().

Micro-optimization.

g_basename() is deprecated in GLib 2.32.  Instead, verify that the
suffix does not have a backslash, to catch Windows path names.