Add basic build-{arch,indep} to fix lintian warnings

W: ppp source: debian-rules-missing-recommended-target build-arch
W: ppp source: debian-rules-missing-recommended-target build-indep
W: ppp source: package-would-benefit-from-build-arch-targets

This is only a very basic change to introduce the build targets in the simplest
possible manner. A more fleshed-out version will be forthcoming in a future
build system overhaul.
Add patch radius-config.c-unkown-typo to fix spelling-error-in-binary

I: ppp: spelling-error-in-binary usr/lib/pppd/2.4.5/radius.so unkown unknown
Add secure-card-interpreter-fix.patch to fix example-wrong-path-for-interpreter

I: ppp: example-wrong-path-for-interpreter
  usr/share/doc/ppp/examples/scripts/secure-card
  (#!/usr/local/bin/expect != /usr/bin/expect)
Remove always_setsid patch (Closes: #598551)
Add Vcs-Browser and Vcs-Git fields pointing to collab-maint/pkg-ppp.git
Enable hardening build flags (Closes: #658181)
Add dh_lintian to debian/rules so we can use overrides