Make some arg const + add autoconf check

configure.ac

@@ -27,6 +27,8 @@ AC_CONFIG_MACRO_DIR([m4])
 
 # Checks for programs.
 AC_GNU_SOURCE
+AC_C_INLINE
+AC_C_CONST
 AC_PROG_CC
 AM_PROG_CC_C_O 
 AC_PROG_MAKE_SET

src/include/ttail_search.h

@@ -91,6 +91,6 @@ const char* ttail_logline_subst(ttail_t*, const char*);
  *@return <0 if a<b, >0 if a>b and 0 if a == b
  *@todo checks
  */
-int ttail_tm_cmp(struct tm*, struct tm*);
+int ttail_tm_cmp(const struct tm*, const struct tm*);
 
 #endif

src/ttail_search.c

@@ -72,7 +72,7 @@ const char* ttail_logline_subst(ttail_t* t, const char* logline)
 	return logline + pmatch[0].rm_eo;
 }
 
-int ttail_tm_cmp(struct tm *ta, struct tm *tb)
+int ttail_tm_cmp(const struct tm *ta, const struct tm *tb)
 {
 	int r;
 	r = ta->tm_year - tb->tm_year;