Function mocSkyProportion( moc )

Description:
Returns the proportion of the sky covered by a given MOC.

If the given moc value does not represent a MOC (for instance no file exists or the file/string is not in MOC format) a warning will be issued the first time it's referenced, and the result will be NaN.

Parameters:
moc (String)
a MOC identifier; a filename, a URL, a VizieR table name, or an ASCII MOC string
Return Value (floating point):
a fractional value in the range 0..1
Signature:
double mocSkyProportion(String)