docs: Rename the .devhelp2 file to match the directory name
docs: Rename the .devhelp2 file to match the directory name

When searching for devhelp books, devhelp expects the .devhelp2 filename
to match the directory name.

Fixes bug 664167.

spidermonkdust/vala,jessevdk/vala,frida/vala,playya/vala,spidermonkdust/vala,playya/vala,flobrosch/vala-fixes,tjol/vala-tjol,Distrotech/vala,Distrotech/vala,frida/vala,severinh/vala,Distrotech/vala,rvu95/vala,jessevdk/vala,playya/vala,xdave/pvala,GNOME/vala,flobrosch/vala-fixes,tjol/vala-tjol,GNOME/vala,GNOME/vala,spidermonkdust/vala,rvu95/vala,severinh/vala,tjol/vala-tjol,frida/vala,GNOME/vala,frida/vala,severinh/vala,rvu95/vala,frida/vala,flobrosch/vala-fixes,jessevdk/vala