Fix for [#7866] Relative Path to library from command line

http://projects.blender.org/tracker/index.php?func=detail&aid=7866&group_id=9&atid=125

where linked relative blend files would not load when the absolute path was not given.
Solved by constructing the absolute path from the command line argument given.

source/creator/creator.c

@@ -688,8 +688,49 @@ int main(int argc, char **argv)
 			}
 		}
 		else {
+			
+			/* Make the path absolute because its needed for relative linked blends to be found */
+			int abs = 0;
+			int filelen;
+			char cwd[FILE_MAXDIR + FILE_MAXFILE];
+			char filename[FILE_MAXDIR + FILE_MAXFILE];
+			cwd[0] = filename[0] = '\0';
+			
+			BLI_strncpy(filename, argv[a], sizeof(filename));
+			filelen = strlen(filename);
+			
+			/* relative path checks, could do more tests here... */
+#ifdef WIN32
+			/* Account for X:/ and X:\ - should be enough */
+			if (filelen >= 3 && filename[1] == ':' && (filename[2] == '\\' || filename[2] == '/'))
+				abs = 1;
+#else
+			if (filelen >= 2 && filename[0] == '/')
+				abs = 1	;
+#endif
+			if (!abs) {
+				BLI_getwdN(cwd); /* incase the full path to the blend isnt used */
+				
+				if (cwd[0] == '\0') {
+					printf(
+					"Could not get the current working directory - $PWD for an unknown reason.\n\t"
+					"Relative linked files will not load if the entire blend path is not used.\n\t"
+					"The 'Play' button may also fail.\n"
+					);
+				} else {
+					/* uses the blend path relative to cwd important for loading relative linked files.
+					*
+					* cwd should contain c:\ etc on win32 so the relbase can be NULL
+					* relbase being NULL also prevents // being misunderstood as relative to the current
+					* blend file which isnt a feature we want to use in this case since were dealing
+					* with a path from the command line, rather then from inside Blender */
+					
+					BLI_make_file_string(NULL, filename, cwd, argv[a]); 
+				}
+			}
+			
 			if (G.background) {
-				BKE_read_file(argv[a], NULL);
+				BKE_read_file(filename, NULL);
 				sound_initialize_sounds();
 
 				/* happens for the UI on file reading too */
@@ -698,7 +739,7 @@ int main(int argc, char **argv)
 			} else {
 				/* we are not running in background mode here, but start blender in UI mode with 
 				   a file - this should do everything a 'load file' does */
-				BIF_read_file(argv[a]);
+				BIF_read_file(filename);
 			}
 		}
 	}