Clean up uses of rtl_ustr_ascii_shortenedCompareIgnoreAsciiCase_WithLength

Change-Id: Ie37614dac882bfe05f8ce595ae6b20326dce872e
Fix construction of non-ASCII test string

Change-Id: I495ba4e2394bf0fd09b4d0f0111f9b8531674733
Adapt rtl_uriConvertRelToAbs to RFC 3986

...which updates RFC 2396, removes the requirement that the base URI's path
starts with a slash, and clarifies how to treat excess "." and ".." segments.

This nicely allows handling of those odd vnd.sun.star.Package URLs as intended
now, so that making <foo> absolute relative to base URL
<vnd.sun.star.Package:Pictures/bar> yields <vnd.sun.star.Package:Pictures/foo>
instead of provoking a MalformedUriException.

Change-Id: Ice84303a57698a2c05d3a45541fe78b67450fa3c