Update .mailmap with recent contributors.

I should have updated everyone who committed since the migration to git (giving me a canonical email).

I've search git shortlog -s to ensure the best I could that there are no duplicate. I discovered that email addresses from the mailmap are uncapitalised whereas the unmodified addresses are not, creating two different authors for no reason. So, I've added some record to normalise the canonical email addresses when needed.
Fixing bug #1758: Print Hint output can be misleading if variable shadows hypothesis.
Follow-up of bugfix for #3204: local definitions were not handled properly.
Fixup make clean and .merlin
Makefiles use $(foo), not $foo, for variables

Also, we need :=, so that it's evaluated immediately, rather than
becoming a self-recursive variable.  This fixes the "Undefined variable
'C'" error that make keeps spewing.
Relaxing the sort elimination check to allow for let-bindings in arities.

I restored this in the kernel, and added it to the checker. There is one last
source of non-uniformity, which is the Sort case in the checker (was not
present in the kernel). I don't know what this case covers, so it should be
reviewed.
Fixing checker compilation, which was broken by the following commit:

05d5f8b9065b0f5e0349cf3d39dd62ab99f30369
Fixing an interpretation bug with tactics in notations. For some obscure
reason, Ltac interpretation does not allow tactics of the following
shape : let x := bla in TacGeneric tac. Hence we force genargs to be
tactics and build the resulting hole tactic from scratch.
Adding a default object to generic argument registering mechanism.
Fixing coqdep graph printing. The transitive reduction algorithm was bugged.
Using full paths in coqdep -dumpgraph.
bug correction in proving principles of function