Find the definition of the FUNCTION near point.
Finds the source file containing the definition of the function
near point (selected by `function-called-at-point') in a buffer and
places point before the definition.
Set mark before moving, if the buffer already existed.
The library where FUNCTION is defined is searched for in
`find-function-source-path', if non-nil, otherwise in `load-path'.
See also `find-function-recenter-line' and `find-function-after-hook'.
(fn FUNCTION)