Add netpbm image size obtaining and resizing

function mew-pbm-size
netpbm (PBM, PGM, PPM, PNM, PAM) formats
Fix indent

function mew-mime-image
Fix indent only. No other changed.
Merge pull request #52 from trueroad/pbm-image-resize

Add netpbm image size obtaining and resizing
removing unnecessary local var.