R1:35d03d36c72a

Improve display behavior of commit messages in Diffusion

Summary:
See T372. Always render commit messages on one display line, so the table
doesn't jump around as they AJAX in on browse views.

The goal here is to have the cell choose a size naturally and for its content to
render with "overflow: hidden" if the natural size isn't large enough to contain
the content. "white-space: pre" or "white-space: nowrap" would prevent wrapping
but potentially make the table exceed the display width when a better…