Coloring error and warning messages in the gui console

[Torsten]

I am currently working on possible ways to color error and warning
messages in the gui console window. The unix based terminal offers
filters for highlighting matched "hotspots". Unfortunately, the elements
painted for highlighting lead to ugly artefacts when scrolling.
Consequently, this filter method is currently only used for underlining
clickable links (files for opening in the editor or urls) when the mouse
cursor is hovering over them.

For the text colors of error and warning messages I would like to insert
suitable escape sequences into the message strings as implemented in the
patch attached to comment #9 of bug #35619
(https://savannah.gnu.org/bugs/?35619#comment9)
Before pushing this patch, I would like to know whether there are any
objections against changing one of octaves core files (error.cc) only
for "cosmetic" reasons.

Best,
Torsten