Simpler build using OCamlMakefile

(cherry-picked from dd9e58d5a0fa7f9f703183d10822eb9df80aa761)
Conflicts:
	Makefile
	README.md
	opam.install
	shell/release.sh
	src/client/opamState.ml
	src_ext/Makefile
	src_ext/depends.ocp.boot
Backporting older dose camlp4-hardcode macro patches

Taken from cd3635e10b1e1195cc6b748cab23ce0427c616ac
Fix travis scripts
Build & travis fixes
Remove prereqs from make 'install*' targets

so that it's safe to call them with 'sudo'
make: Install libs to the ocamlfind prefix rather than $(prefix)
Fixed the 'test' and 'doc' targets
Remove -warn-error in the Makefile version too.

Followup to 1e2b8cc677942ba56301781107dcf841f0d849a7 which removed
them for ocp-build
Makefiles: handle DESTDIR

Closes #1369
Small Makefile fixes
Update CHANGES for 1.1.1 backport (from 1.2)
Add workaround bug #1355 in opam-installer

the real fix runs deeper than is sane backporting, and we're just interested
in having the Makefile work
travis: use branch 1.1 of opam-rt
Merge pull request #1424 from OCamlPro/1.1-build-backport

1.1 build backport