add an updatebounding rectangle method to vertexdrawable
add an updatebounding rectangle method to vertexdrawable

this can be used when something within the library needs to redraw the vertex
drawable for whatever reason

Signed-off-by: Sam Phippen <e5a09176608998a68778e11d5021c871e8fae93c@googlemail.com>

samphippen/spe,samphippen/spe,samphippen/spe,samphippen/spe