Create a C++ wrapper for unixtodstr()

No need to use time32_t for this.

src/sbbs3/sbbs.h

@@ -823,6 +823,7 @@ public:
 	char*	server_host_name(void);
 	char*	timestr(time_t);
 	char*	datestr(time_t, char* str = nullptr);
+	char*	unixtodstr(time_t, char* str = nullptr);
 	char	timestr_output[60]{};
 	char	datestr_output[60]{};
 	char*	age_of_posted_item(char* buf, size_t max, time_t);

src/sbbs3/str.cpp

@@ -983,6 +983,13 @@ char* sbbs_t::datestr(time_t t, char* str)
 	return ::datestr(&cfg, t, str);
 }
 
+char* sbbs_t::unixtodstr(time_t t, char* str)
+{
+	if(str == nullptr)
+		str = datestr_output;
+	return ::unixtodstr(&cfg, t, str);
+}
+
 void sbbs_t::sys_info()
 {
 	char	tmp[128];