This solves a long-standing problem whereby relative paths are not
properly resolved, leading to incorrect symbol conflicts when relative
paths to the same package vary between two imports.
See doc/notes/path-processing for an illustration.
* src/current/include/preproc/path.xsl
(preproc:resolve-relative-import): Add function.
(preproc:resolv-path, preproc:resolve-path, preproc:get-path): Add
functions to invoke existing templates.
* src/current/include/preproc/symtable.xsl (preproc:symimport): Use
`preproc:resolve-relative-import'.
* doc/notes/path-processing: Add notes.