Document environment variables in their own section
Closes #1066
Attempt `-p` parameters to the `patch` command until 5
Fixes #113
Improve some error messages with malformed files
(much more useful when you are given the incriminated file name)
Backported improved sanitization/quoting when calling external solver from dose.
Do not use which when trying to locale aspcud.
Merge pull request #1124 from vbmithr/nowhich

Do not use which when trying to locale aspcud.
Merge pull request #1115 from AltGr/man-env-vars

Document environment variables in their own section
Merge pull request #1117 from AltGr/patch-level-try-again

Attempt `-p` parameters to the `patch` command until 5
Merge pull request #1118 from AltGr/improve-file-errmsg

Improve some error messages with malformed files
Turning the 'NOTE: blah exists although blah is not installed' into debug
Closes #1111
overriding archive files from the package is not really a warning
Merge pull request #1123 from rdicosmo/sanitize

Backported improved sanitization/quoting when calling external solver from dose
Merge pull request #1116 from AltGr/blah-to-debug

Turning the 'NOTE: blah exists although blah is not installed' into debug
Release: allow `make` to be overridden via the `MAKE` env var

This is required for the BSDs, where GNU make is installed as `gmake`.
Merge pull request #1130 from avsm/master

Release: allow `make` to be overridden via the `MAKE` env var
Refactor opam variable resolution, and add new variables
Variable resolution in opam files

The behaviour has slightly changed, but should be more powerful and the code much clearer:
- in the opam file of `pkg`, `%{variable}%` will now be understood as `%{pkg:variable}%``
- the information returned (eg. version) corresponds to the current opam file if relevant, OR to the installed version of the named package

Todo:
- fix the manual accordingly
- fix `opam config var list`. We probably don't want every var for every package there.
- extend the compilation environment to make the new variables accessible from the build scripts ? (probably not for costly ones
Fix the 'version' variable for pinned packages
Fixed the 'hash' variable
Rewriting variables in post-messages
Closes #989