After testing under Windows, I've committed my proposed solution to the URI escaping issues in pathnames to the trunk as [r13506][1]. If fellow developers could build and test the ABCL-TEST-LISP system on their respective systems, I would appreciate it.
From the commit message:
Fix problems with #\Space characters in JAR pathnames.
We now require that inputs to the PATHNAME routines that have the URI scheme "jar:file" or "file" properly encode themselves as URIs according to RFC2396. Mainly this means that #\Space and #? characters in such strings should be percent encoded (i.e. "jar:file:/path%20with%20/space/and%3fquestion-mark"). The corresponding namestring routines have been adjusted to output such URI encoded representations, although the underlying PATHNAME objects contain unescaped values. The routines for loading FASLs have been adjusted to URI encode their inputs as well.
The #+ character is no longer an escape for #\Space (this was a bug).
[1]: http://trac.common-lisp.net/armedbear/changeset/13056