SASL support

The only supported methods are PLAIN and EXTERNAL, the latter is untested as of
now.
The code gets the values from the keys named sasl_{mechanism,username,password}
specified for each chatnet.

src/irc/core/Makefile.am

@@ -27,6 +27,7 @@ libirc_core_a_SOURCES = \
         irc-servers-setup.c \
         irc-session.c \
         irc-cap.c \
+        sasl.c \
         lag.c \
         massjoin.c \
         modes.c \
@@ -50,6 +51,7 @@ pkginc_irc_core_HEADERS = \
         irc-servers.h \
         irc-servers-setup.h \
         irc-cap.h \
+        sasl.h \
         modes.h \
         mode-lists.h \
 	module.h \