the created locks only uses the tileset name and the tile's xyz. there can be potential issues with overlapping locks

marking as low priority, as: - the consequences are low-key: a user might get back an error report if a clash has occured, but a following request will succeed. - this is only triggered if the tileset has multiple grids or multiple dimensions - the occurence should be rather low, there must be two distinct client requesting the same unseeded xyz tile with a different grid or dimension

solution is to add grid name and dimension to the name of the semaphore created by sem_open(). this isn't as straightforward as it seems, as some systems have a limit on the number of characters a semaphore name can contain (14 is the minimum)

This issue was closed by revision r181.