syslog-ng.h: remove DMALLOC macros

dmalloc has not been support for a long time, its configure.ac counterpart
has already been removed, remove the stuff from syslog-ng.h too.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
configure.ac: break up AC_CHECK_HEADERS to one header per line

To make it easier to extend the list and cause less conflicts.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
configure.ac: break up AC_CHECK_FUNCS to one function per line

To make it easier to extend the list and cause less conflicts.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>