Protect against timeout during manual refresh

Greetings.

In using the feedapi module with my own custom parser and processor, I've run into a bug when refreshing a feed manually (by clicking the 'Refresh' tab on the node page view of a feedapi enabled node).

Basically, there are too many items in my feed for the refreshing to finish within the default 30 second PHP timeout. The function in feedapi that is called to refresh items (_feedapi_invoke_refresh()) takes a special parameter to indicate whether the refresh is part of cron job. If it is, then the code takes special precautions to make sure that the feed will take no more than it's configured % share of the cron exeuction time.

However, there's no similar check if the call to this function is the result of something other than cron (in this case, a manual refresh of the feed).

This patch adds code that changes the _feedapi_invoke_refresh() function to apply a similar logic to manual refreshes. If a PHP timeout is 5 seconds away, the function breaks out of the loop similar to the way _feedapi_node_purge() (in feedapi_node.module) breaks out of its loop when it can't purge all items from a feed within the PHP timeout.

To achieve this, I changed the code to call feedapi_cron_time() for manual refreshes.

feedapi_cron_time() calculates the time remaining for a feed's refresh during a cron job. I changed the name of this function to feedapi_time_remaining() since this patch results in its use for manual refreshes and I also added a parameter for a boolean to indicate whether or not this function should be computing the time remaining for a feed refresh during a cron job. If not, it calculates the time remaining until there is only 5 seconds left before a timeout.

-Ankur