De-emphasize lines that didn't execute

[Botond Ballo]

Lines that didn't execute are currently highlighted in red, which visually emphasizes them over lines that executed. We actually want the reverse, to de-emphasize such lines, e.g. by printing them with a gray foreground color.

Note that "lines that didn't execute" can include lines that control flow did conceptually "flow over", but just didn't involve actual execution (e.g. blank lines, comment lines, lines containing compile-time-only declarations, etc.).

[Derek Berger]

de-emphasize unexecuted lines (fixes #5)

→ <<cset bb5a941b6cee>>