more nuanced treatment of -L and RPATHs
more nuanced treatment of -L and RPATHs

Before this patch, if given a -L, the world looked like this:

|            | install | not install |
|------------+---------+-------------|
| /usr/lib   | ERROR   | rpath       |
| /usr/lib/X | ERROR   | rpath       |
| /opt/X     | ERROR   | rpath       |

I.e. no -L allowed at packaging-time, and all -L made an RPATH. Now I'm more
careful:

|            | install  | not install |
|------------+----------+-------------|
| /usr/lib   | no rpath | no rpath    |
| /usr/lib/X | no rpath | no rpath    |
| /opt/X     | ERROR    | rpath       |

RPATHs are ONLY made for non-standard paths and only those cause install-time
failures

dkogan/buildsystem,dkogan/buildsystem