059d-dc42 release

1. Reworked network layer to be more robust in the presence of network
errors (hopefully). In particular, don't release transmit buffers if
they might still be needed to retry sending data because the ACK got
lost.
2. Fixed bug whereby fileinfo command looked for the print height and
filament used if the extensio was .gcode or .gc or .gco but not if it
was .g.
3. When the M25 (pause print) command is received, pause the current
gcode so that commands such as M116 (wait for temperatures) can be
interrupted.
Allow network requests to span multiple TCP pkts

Incoming network requests can now span multiple TCP messages. Max upload
buffer increased to 2048. Also return layerHeight and generatedBy values
when asking for fileinfo on a gcode file. This is an interim commit that
needs cleaning up before release.
Support HTTP requests longer than TCP MSS

Changed webserver to support HTTP requests that span multiple TCP
messages. Changed upload code to to block file writes direct fro the
received message. Increased maximum upload message size. Changed
fileinfo command to report layer height and what program generated the
gcode file, if available.
Merged RepRapRro's 0.65e version in

Merged changes (mostly to handle multiple tools i.e. extruders) from
RRP's 0.65e version.
Merge remote-tracking branch 'dc42/duet' into duet
Increased FTP upload buffer to 3000 bytes