Writing to the lockfile

[richfitz]

Could be solved by use of a global counter and a bit of hackery, without having to create a full connection object.

• run normalizePath(filename, mustWork=FALSE) to get the complete filename (hopefully).
• increment a global counter stored in a package environment with this name
• if the counter increments from zero create the handle for real:
  • run file(filename, mode="a") to create a proper R connection
  • run seagull_open() to get the actual file descriptor ("handle")
  • save both with the counter, and return a list: list(filename, connection, handle)
• if the counter exists return the previous version without opening anything

On release we decrement the counter and if it hits zero:

1. close the real file
2. close the handle
3. delete the global counter.