Prevent possible crash when rendering a marker
Merge pull request #1894 from tambry/MarkerCrashFix

Prevent a possible crash when rendering a marker
Fixed gate extension ids synchronization, for #1895.
Added a new concept of NetworkId, allowing to transfer ids over the network
instead of strings.
RPCs are now all handled the same way (except RPC Pipes, to be completed when
actually used).
Merge branch '6.1.x' of github.com:BuildCraft/BuildCraft into 6.1.x
Merge branch '6.0.x' into 6.1.x
fixed indentation
removed PacketCoordinates from mapped packets, as it's only derived
Gates are now specifically providing actions specific to their side,
for #1895.
implemented close pipe action, close #1902
Started work on actions to provide / request items, for #1877.
Generalized latency property, for #1873
Kill path finding jobs upon interruption, for #1873.
separate normal terminaison from abort
Fixed writing of polymorphic classes.
Fixes #1903 and probably many others.
Added a limit to block scanning. For #1873
Fixed ghost facades from pre-6.0.x
Merge pull request #1905 from tambry/facadeLoadFix

Fixed ghost facades from pre-6.0.x worlds
Started work on carrier robot, for #1907.
fixed style
Fix ghost facades from pre-6.0.x worlds

Essentially same as #1905