tighter scope for no strict refs
dev/build.pl: detect NO MAGIC marker
refactored _image_info_for_format out of image_info

_image_info_for_format and _source are now documented as some
sort of a "friend" function.
Image::Info::WBMP
added test wbmp image

This is bbbike/images/bw_hleft.wbmp
test script for WBMP
skip wbmp in string.t (magic-less files cannot be tested here)
rebuild Image::Info with WBMP entry
updated MANIFEST
release note for 1.33_51
Merge branch 'wbmp'