Return object index from EN_addnode and EN_addlink (issue #432)

Adds an output argument to EN_addnode and EN_addlink that returns the index of the newly added object.
Also refactors the validity check on object ID names.

src/project.c

@@ -7,7 +7,7 @@
  Authors:      see AUTHORS
  Copyright:    see AUTHORS
  License:      see LICENSE
- Last Updated: 04/03/2019
+ Last Updated: 04/18/2019
  ******************************************************************************
 */
 
@@ -988,6 +988,18 @@ int setcomment(Network *network, int object, int index, const char *newcomment)
     }
 }
 
+int namevalid(const char *name)
+//----------------------------------------------------------------
+//  Input:   name = name used to ID an object
+//  Output:  returns TRUE if name is valid, FALSE if not
+//  Purpose: checks that an object's ID name is valid.
+//----------------------------------------------------------------
+{
+    size_t n = strlen(name);
+    if (n < 1 || n > MAXID || strpbrk(name, " \";")) return FALSE;
+    return TRUE;
+}
+
 char *getTmpName(char *fname)
 //----------------------------------------------------------------
 //  Input:   fname = file name string