Curl_unix2addr: avoid using the variable name 'sun'

I suspect this causes compile failures on Solaris:

Bug: http://curl.haxx.se/mail/lib-2014-12/0081.html

lib/curl_addrinfo.c

@@ -488,7 +488,7 @@ Curl_addrinfo *Curl_str2addr(char *address, int port)
 Curl_addrinfo *Curl_unix2addr(const char *path)
 {
   Curl_addrinfo *ai;
-  struct sockaddr_un *sun;
+  struct sockaddr_un *sa_un;
   size_t path_len;
 
   ai = calloc(1, sizeof(Curl_addrinfo));
@@ -500,7 +500,7 @@ Curl_addrinfo *Curl_unix2addr(const char *path)
   }
   /* sun_path must be able to store the NUL-terminated path */
   path_len = strlen(path);
-  if(path_len >= sizeof(sun->sun_path)) {
+  if(path_len >= sizeof(sa_un->sun_path)) {
     free(ai->ai_addr);
     free(ai);
     return NULL;
@@ -509,9 +509,9 @@ Curl_addrinfo *Curl_unix2addr(const char *path)
   ai->ai_family = AF_UNIX;
   ai->ai_socktype = SOCK_STREAM; /* assume reliable transport for HTTP */
   ai->ai_addrlen = (curl_socklen_t) sizeof(struct sockaddr_un);
-  sun = (void *) ai->ai_addr;
-  sun->sun_family = AF_UNIX;
-  memcpy(sun->sun_path, path, path_len + 1); /* copy NUL byte */
+  sa_un = (void *) ai->ai_addr;
+  sa_un->sun_family = AF_UNIX;
+  memcpy(sa_un->sun_path, path, path_len + 1); /* copy NUL byte */
   return ai;
 }
 #endif