Build-depend on valac instead of valac-0.18

[Jeremy Bícha]

vala-0.18 has been dropped from Debian and I expect we'll be able to drop it from Ubuntu before 13.10 is released.

I tried looking at submitting a merge proposal for this but I couldn't figure out how to build with --enable-docs to test what needs to be done for the valadoc part of configure.ac.

At least as built on Ubuntu, it looks like the dependency on libvala-0.18-dev isn't necessary so replacing it and valac-0.18 with just valac should be fine.

I successfully test-built against valac but dbus-test-runner doesn't work right here so I can't tell whether the tests still pass or not.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: libfriends0 0.1.2daily13.06.07-0ubuntu1
ProcVersionSignature: Ubuntu 3.9.0-7.15-generic 3.9.7
Uname: Linux 3.9.0-7-generic x86_64
ApportVersion: 2.10.2-0ubuntu2
Architecture: amd64
Date: Mon Jun 24 13:32:11 2013
InstallationDate: Installed on 2013-06-14 (10 days ago)
InstallationMedia: Ubuntu-GNOME 13.10 "Saucy Salamander" - Alpha amd64 (20130613)
MarkForUpload: True
SourcePackage: libfriends
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

This bug was fixed in the package libfriends - 0.1.2+14.10.20140709-0ubuntu1

---------------
libfriends (0.1.2+14.10.20140709-0ubuntu1) utopic; urgency=medium

  [ Ken VanDine ]
  * debian/control
    - build depend on valac instead of valac-0.18 and dropped
      libvala-0.18-dev (LP: #1194211)
 -- Ubuntu daily release <email address hidden> Wed, 09 Jul 2014 18:14:54 +0000