Fix: the LCOV report code assumed that a branch line that took no branches
meant that the entire line was unexecuted. This isn't true in a few cases:
the line might always raise an exception, or might have been optimized away.
Fixes issue 1896_.
Fix: similarly, the HTML report will now explain that a line that jumps to
none of its expected destinations must have always raised an exception.
Previously, it would say something nonsensical like, "line 4 didn't jump to
line 5 because line 4 was never true, and it didn't jump to line 7 because
line 4 was always true." This was also shown in issue 1896_.
