my first take at documenting the curl_off_t situation when doing an upgrade

   curl_off_t explained

   ====================

curl_off_t is a data type provided by the external libcurl include headers. It

is the type meant to be used for the curl_easy_setopt() options that end with

LARGE. The type is 64bit large on most modern platforms.

Transition from < 7.19.0 to >= 7.19.0

-------------------------------------

Applications that used libcurl before 7.19.0 that is rebuilt with a libcurl

that is 7.19.0 or later may or may not have to worry about anything of

this. We have made a significant effort to make the transition really seamless

and transparant.

You have have to take notice if you are in one of the following situations:

o Your app is using or will after the transition use a libcurl that is built

  with LFS (large file support) disabled even though your system otherwise

  supports it.

o Your app is using or will after the transition use a libcurl that doesn't

  support LFS at all, but your system and compiler support 64bit data types.

In both these cases, the curl_off_t type will now (after the transition) be

64bit where it previously were 32bit. This will cause a binary incompatibility

that you MAY need to deal with.

Historicly

----------

Previously, before 7.19.0, the curl_off_t type would be rather strongly

connected to the size of the system off_t type, where currently curl_off_t is

independent of that.

The strong connection to off_t made it troublesome for application authors

since when they did mistakes, they could get curl_off_t type of different

sizes in the app vs libcurl, and that caused strange effects that were hard to

track and detect by users of libcurl.