Make warning CXXFLAGS configurable

This turns off -Werror by default except in the Debian package.
-Werror is inherently unportable and breaks things on OS X.  While it
can cause problems in Debian too, this is at least a little better.

It also turns off -pedantic in src/protobufs, because apparently
protoc output doesn’t compile with -pedantic on all platforms.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

debian/control

@@ -2,7 +2,7 @@ Source: mosh
 Section: net
 Priority: optional
 Maintainer: Keith Winstein <keithw@mit.edu>
-Build-Depends: debhelper (>= 7.0.0), autotools-dev, protobuf-compiler, libprotobuf-dev, dh-autoreconf, pkg-config, libutempter-dev, libboost-dev, zlib1g-dev
+Build-Depends: debhelper (>= 7.0.50), autotools-dev, protobuf-compiler, libprotobuf-dev, dh-autoreconf, pkg-config, libutempter-dev, libboost-dev, zlib1g-dev
 Standards-Version: 3.9.3
 Homepage: http://mosh.mit.edu
 Vcs-Git: git://github.com/keithw/mosh.git

debian/rules

@@ -11,3 +11,7 @@
 
 %:
 	dh $@ --with autoreconf
+
+override_dh_auto_configure:
+	dh_auto_configure -- \
+		--enable-compile-warnings=error