Enhancement: easier use for ly:expect-warning

[Simon Albrecht]

Hello,

is it imaginable to change ly:expect-warning so that it’s possible to 
use any part of the warning string?
For example, with the ‘kneed beam’ warning
‘no viable initial configuration found: may not find good beam slope’
it’s possible to use
#(ly:expect-warning "no viable")
but it would be nicer to use
#(ly:expect-warning "beam slope")

Though it’s more of a cosmetic change.

Yours, Simon