libDtSvc: Resolve 89 compiler warnings.

cde/lib/DtSvc/DtUtil2/EnvControl.c

@@ -443,7 +443,7 @@ _DtEnvControl(
 				 * then put our dt string just ahead of 
 				 * "/usr/bin/X11" in the new PATH 
 				 */
-				 *(ptr - 1) = NULL; 
+				 *(ptr - 1) = '\0'; 
 				 sprintf(_postDtEnvironment.binPath,
 				   "%s=%s:%s:%s",
 				    BIN_PATH_ENVIRON,
@@ -479,7 +479,7 @@ _DtEnvControl(
 				 * "/usr/bin" in the new PATH 
 				 */
 
-				 *(ptr - 1) = NULL; 
+				 *(ptr - 1) = '\0'; 
 				 sprintf(_postDtEnvironment.binPath,
 				   "%s=%s:%s:%s",
 				    BIN_PATH_ENVIRON,

cde/lib/DtSvc/DtUtil2/SmCreateDirs.c

@@ -265,7 +265,7 @@ GetShortHostname(
    if (status = gethostname(buffer, bufsize))
       return status; /* failed gethostname */
    if (ptr = strstr(buffer, (char *)"."))
-      *ptr = NULL;  /* delete domain name if there is one */
+      *ptr = '\0';  /* delete domain name if there is one */
    return 0;
 }
 

cde/lib/DtSvc/DtUtil2/XlationSvc.c

@@ -259,7 +259,7 @@ char * ExpandPath (
     /*** otherwise, make it relative to the current directory ***/
 
     /* get user's current working directory */
-    if (getcwd(tmpPath, MAXPATHLEN) == NULL) return NULL; /* RETURN: error */
+    if (getcwd(tmpPath, MAXPATHLEN) == 0) return NULL; /* RETURN: error */
 
     /*** add a slash to end of path component, if needed ***/
     /* get end of the string */

cde/lib/DtSvc/DtUtil2/addToRes.c

@@ -564,7 +564,7 @@ _DtAddResString(
     int                 actualFormat;
     unsigned long       nitems, leftover;
 
-    if((data == NULL) || (*data == NULL))
+    if((data == NULL) || (*data == '\0'))
     {
 	return;
     }