[PATCH 0/4] Fewer calls to "open" when stepping

[Tom Tromey]

A user noticed that gdb calls open very many times while stepping.

This series improves gdb's behavior by changing the source cache to
also cache un-highlighted text, and to track the "line_charpos" data
that is currently put into the symtab.  It also includes a patch to
fix an apparently longstanding logic bug in the source file error
reporting.

Tested on x86-64 Fedora 29.

Tom