Allow tilde expansion for fields in .linesrc

[memmerto]

Tilde expansion in fields in .linesrc (and probably other places) does not work.
This is unexpected and confusing and should be fixed.
(See LINES-L on 2020-04-05 for an example.)

[tfmorris]

I suspect "unexpected" is a generational thing. Traditionally, tilde expansion is done by the shell on Unix systems and basic C programs don't understand the concept.

As an aside, some (all?) implementations of libc's wordexp actually invoke /bin/sh in a subprocess to get this expansion done, so not super fast.