Build with Vala 0.22.1 (ASCII string binding issue): Bug #739470
Build with Vala 0.22.1 (ASCII string binding issue): Bug #739470

ASCII strup/strdown not bound in Vala 0.22 or 0.24, so need to use
externs to import those symbols until Vala 0.26 is the minimum
requirement.

AtticHacker/geary,tshikaboom/geary,glebihan/geary,aatishnn/geary,mjog/geary,jimbonator/geary,githubnemo/geary,aatishnn/geary,tshikaboom/geary,jimbonator/geary,glebihan/geary,robol/geary,tshikaboom/geary,martinra/geary,glebihan/geary,jimbonator/geary,martinra/geary,emersion/geary,AtticHacker/geary,mjog/geary,emersion/geary,AtticHacker/geary,emersion/geary,githubnemo/geary,githubnemo/geary,mjog/geary,aatishnn/geary,robol/geary,robol/geary,martinra/geary