[postgis-devel] line_substring() function

[strk at refractions.net]

I've implemented a line_substring(geometry, float8, float8) function
returning a subset of the input linestring starting and ending at
the given fractions of total length (numbers between 0 and 1).

This has been done to generalize the:
	line_interpolate_line(geometry, proportion, direction)
function listed in the TODO file. The direction in this
case is not taken into cosideration, but you can still use 
the reverse() function on either input or output.

Code and docs in HEAD branch.

--strk;