Add codes that convert from emacs unsupported formats to inline images

Bmp etc. to pnm / pam by netpbm image converting tools.
Merge pull request #48 from trueroad/unsupported-image-convert

Add codes that convert from emacs unsupported formats to inline images
Add bmp image size obtaining and resizing

function mew-bmp-size
Merge pull request #49 from trueroad/bmp-image-resize

Add bmp image size obtaining and resizing
Add internet media types of netpbm formats

image/x-portable-bitmap pbm
image/x-portable-graymap pgm
image/x-portable-pixmap ppm
image/x-portable-anymap pnm
image/x-portable-arbitrarymap pam
Fix function mew-image-inline-p return value

function mew-image-inline-p may return strings.
It should return value t or nil only.
Merge pull request #50 from trueroad/pbm-type

Add internet media types of netpbm formats
Merge pull request #51 from trueroad/patch-5

Fix function mew-image-inline-p return value
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.
Add emacs unsupported image resizing

Emacs unsupported image size is obtained
after converting the image to PNM (pbm) format.
Merge pull request #53 from trueroad/unsupported-image-resize

Add emacs unsupported image resizing
Merge branch 'master' into nagao-oresama-branch