Commit 3d6bbbe9 made "config -list" print strings in quotes to avoid
the strings being interpreted as terminal escape codes. This commit
does the same for "source-list-line-color", which is a raw interface.
This fixes "config -list" with a config like
source-list-line-color: "\x1b[34m"
The "int" variant is already printed correctly, so just use the
default case for that.