#1 Rotate of +/-90 +/- 180 renders improper

[Anonymous]

The rotate operation for +/- 90 or +/- 180 gives
improper results.
It seems to use some complex render function which adds
small
mistakes (looks like you render-rotate it 89 or 91). It
should use
some simple mechanism like a flip for 90 values.
This bug makes it impossible to rotate small arrow
buttons of slider for
example.

The flip function also seems to move the whole image
one pixel up
or down after the calculate operation.