common: constify init_log filename argument

Signed-off-by: Kevin Shanahan <kmshanah@disenchant.net>

common/log.c

@@ -32,7 +32,7 @@ static FILE *logfile;
 static qboolean log_ok;
 
 void
-init_log(char *filename)
+init_log(const char *filename)
 {
     log_ok = false;
     if ((logfile = fopen(filename, "w")))

include/common/log.h

@@ -30,7 +30,7 @@
 #include <stdio.h>
 #include <common/cmdlib.h>
 
-void init_log(char *filename);
+void init_log(const char *filename);
 void close_log();
 void logprint(const char *fmt, ...) __attribute__((format(printf,1,2)));
 void logvprint(const char *fmt, va_list args) __attribute__((format(printf,1,0)));