Fix most `wider type truncated to int' bugs on OSF1 due to implicit decls:

 #include <stdlib.h>    to get malloc & co various places,
 #include <ac/string.h> to get strlen & co in (liblutil/setproctitle.c),
 declare ch_malloc & co (slurp.h), avl_find_lin (avl.h), Malloc (ud/edit.c).
Also changed ch_malloc & co from char* to void* functions.