In effect, this adds PIE and RELRO to binaries.

Doveadm-sieve plugin may be broken at this point; not tested so far.

http://dovecot.org/patches/2.2/doveadm-sieve-plugin.diff
Made some small modifications.
This code should not interfere with normal ManageSieve operation, so I commit this right now without much testing.
The actual doveadm sieve plugin has a few open issues that need to be resolved still.

Changed result execution logging to use a var_expand_table created by liblda to avoid code duplication (patch by Timo Sirainen).

Let configure automatically infer path to installed Dovecot and don't rely on installed libtool .la files anymore (patch by Timo Sirainen).