Handle postgresql and sqlite3 libs properly

Do not fail to compile when one of them is missing but the other one is not.

Raise an error when trying to open a database with the missing library.

see #3237

Merge branch 'postgresql' into 'postgresql'

Some fixes for the postgresql branch

See merge request louiz/biboumi!19

Actually free the database on Database::close()

.release() returns the pointer and releases ownership *without*
destruction.

Make destructor of DatabaseEngine virtual

Make destructor of Statement virtual

I got an ASAN error otherwise (type mismatch)

Support for full postgresql URIs

(cf. https://www.postgresql.org/docs/9.4/static/libpq-connect.html#LIBPQ-CONNSTRING)

Add postgresql support

Send \r\n at the end of the identd responses

fix #3315

Add an e2e test to demonstrate #3304

Fix #3304

Change how we count the number of connected resources to a server

Add a workaround for https://github.com/randombit/botan/issues/1276

ref #3278

Release version 6.1

Update changelog for version 6.1

Explicitely include all needed botan headers

Most importantely, include parsing.h, since read_cfg is not implicitely
included anymore in botan 2.3, and that does not compile.

Also do not included botan.h anymore, since it’s deprecated in botan 2.3

fix #3296

Remove a redundant Body definition

Fix a little formatting issue in the changelog

Merge branch 'patch-1' into 'master'

Stop allowing the 1024-bit for irc.ppirc.net

See merge request louiz/biboumi!16

Merge branch 'v6' into 'master'

compat: revert to using sqlite's close() function for compat with older distros.

See merge request !17

compat: revert to using sqlite's close() function for compat with older distros.
 close_v2(), in use before this commit, was introduced as part of sqlite 3.7.14
 (2012-09-03), and is as such incompatible with debian wheezy (3.7.13) and
 centos6 (3.6.20).
 FTR, Wheezy will be supported until May 2018, and centos6, until November 2020.