Slow down of TextMorph

[hilaire]

TextMorph are slow due to unnecessary update of its cached bitmap when sending message #contents:

Change it as follow:

DrGTextMorph>>contents: stringOrText
 self contents = stringOrText ifTrue: [ ^ self ].
 myForm := nil.
 ^ super contents: stringOrText

Caution, it may conflict with TextMorph at font size change; indeed its bitmap cache need to be reset although content text does not change.