m_callerid Fix bookkeeping error introduced when unserializing callerid_data

This also fixes a memory leak that didn't occur naturally but was triggerable by remote servers

Thanks to @SimosNap for the report
m_callerid Ignore duplicate entries when unserializing callerid_data
m_spanningtree Fix IS_LOCAL() check in OnRehash handler
m_callerid Allow messaging yourself while +g regardless of the ACCEPT list
m_ident Invalidate cache after changing User::ident
Fix uuids getting truncated in the nick hash in UserManager::AddUser() if nickmax is < 9
Immediately stop processing whenever we detect and handle a RecvQ overrun

Thanks to @SimosNap for the report and cooperation
Don't crop the channel name if it's too long in Channel::Channel()

...and especially don't use the shortened name in one place and the original in another

Having different <limits:maxchan> values on the same network is not supported
m_permchannels Workaround for alphabetical module initialization order

Read database after all modules have been inited
Add exception logging

Fixes #485 reported by @gholms
Log some internal errors on DEFAULT loglevel instead of DEBUG, log detected errors in m_callerid
m_filter Fix memory leak on unload
m_filter, m_rline Remove rlines and filters when the regex engine changes or becomes unavailable
m_rline Switch to OnUserRegister hook to disconnect banned users earlier
Add config option to disable somaxconn range() check
m_spanningtree Fix crash when connecting to a remote server that has the same name as we do and also there is a link block with our server name and their password

See 49223cfe12ecd9071123f724e615e63841f2421d
m_ssl_gnutls Add ability to load DH params from file

This greatly decreases the load time because the DH parameters no longer have to be (re)generated each time the module is loaded
Move SocketEngine::IgnoreError() code into socketengine.h and add test for EWOULDBLOCK
Release 2.0.12
Fix a few minor issues with `make distclean`.

- Only remove the base directory for in-source installs.
- Use full paths to the source directory.
- Update the help message to be more accurate.
Merge pull request #509 from SaberUK/insp20+make-distclean

Fix a few minor issues with `make distclean`.