Add dependencies for the libphonenumber6-dev package.

The dependencies for this package should be those packages that must be
installed in order to compile and link code that uses the library.

R=daniel@pocock.pro
BUG=

Review URL: https://codereview.appspot.com/137740043

debian/control

@@ -51,7 +51,11 @@ Architecture: any
 Provides: libphonenumber-dev
 Conflicts: libphonenumber-dev
 Replaces: libphonenumber-dev
-Depends: libphonenumber6 (=${binary:Version}), ${misc:Depends}
+Depends: libphonenumber6 (=${binary:Version}), ${misc:Depends},
+         libboost-dev (>= 1.40),
+         libboost-system-dev (>= 1.40),
+         libboost-thread-dev (>= 1.40),
+         libprotobuf-dev (>= 2.4)
 Description: parsing/formatting/validating phone numbers - development files
  Google's common C++ and Java library for parsing, formatting, storing and
  validating international phone numbers.