Based on report by scan-build.

plugins: lda-sieve: lda-sieve-plugin - Make sure context structure does not retain dangling pointers

Based on report by scan-build.

plugins: imapsieve: imap-sieve - Make sure imap_sieve_handle_exec_status() is not called with rscript == NULL

Based on report by scan-build.

Found by scan-build.

kill() needs this include on many platforms.

lib-sieve: plugins: vacation: ext-vacation-settings - Reduce default sieve_vacation_max_period to 60 days from infinity

lib-sieve: plugins: spamvirustest: ext-spamvirustest-settings - Use ENUM type for status_type settings

lib-sieve: plugins: spamvirustest: Drop useless config example comment in ext-spamvirustest-settings.c

This is needed for getting sieve_extensions defaults when running with -O
parameter to disable reading configs.

Also rename sasl_mech to auth_sasl_mechanisms.

SASL binding is now used if ldap_sasl_mech is non-empty.

The HAVE_SASL_*H macros were not visible, so the SASL settings were never
enabled.

With this change the ldap settings are included in the main pigeonhole
settings plugin. Since it doesn't require linking with ldap library,
this works well enough. Even further split could be still done by
moving the ldap settings into its own settings plugin.