Pack libjpeg in "extern C", since not all platforms have this in the header.
Pack libjpeg in "extern C", since not all platforms have this in the header.

git-svn-id: 04e88ac4940b0408b73cd6f458a224a262abaaff@497 ec705bc8-faf6-4f9b-9aff-b4916e9bedc3

jbuchbinder/rawspeed,jbuchbinder/rawspeed