2.13.48 regtests

[Keith OHara]

My issue-1500 patch slightly increased horizontal spacing in several regtests
(reversing some of the tightening seen in the change from 2.13.24 to .25)

I changed 'lyrics-melisma-beam.ly' to make it more sensitive to spacing bugs 
similar to issue 1200.

Pál changed 'mensural-ligatures.ly' and perhaps can comment on whether the new 
output is what he intended.

Han Wen changed the placement of tremolo bars between semibreves, whole notes.

I see nothing surprising.