smurf: Indent continuation of multi-line prototype
smurf: Use zero-based numbering for JSA tiles
smurf: Refer to HEALPix facets as such

This is to avoid confusion between HPX (the FITS algorithm
code) and HEALPix itself (the scheme).
smurf: Correct spelling of the
smurf: Correct JSA x,y tile indices from i2xy

The documentation says that the xt and yt values returned
by smf_jsatilei2xy are zero-based, but they were having
one added to them.
smurf: Remove duplicate JSA tile i2xy code

The smf_jsatileheader function can use smf_jsatilei2xy
to convert tile numbers to x and y coordinates. This
required the addition of the tile index return parameter
to smf_jsatilei2xy which also prevents the lower left
tile being split.  If necessary this behaviour could be
controlled by a separate parameter.  Since smf_jsatilei2xy
checks that the tile number is valid, smf_jsatileheader
need no longer do so.
smurf: Index JSA tile facets as defined by HEALPix

The HEALPix paper (Gorsky et. al. 2005 ApJ 622, 759) defines the
numbering scheme to be used for the base resolution pixels (facets).
This commit adjusts the numbering of the facets to follow this
scheme.  This is the first step towards numbering the JSA
tiles using the HEALPix nested numbering scheme, which was
an action item from the JSA meeting of 2013-10-28.
smurf: Nested indexing of JSA tiles within facets

The tiles within each HEALPix base resolution pixel (facet)
are now numbered using the nested scheme described in the
HEALPix paper.  The offsets north-east and north-west from
the southern corner of the facet are represented by the
even (including 0th) and odd bits respectively.  This,
together with the previous commit, completes the action
item from the JSA meeting on 2013-10-28 of applying the
standard HEALPix nested numbering scheme to the JSA tiles.
smurf: Skip bad tile values in initial region mesh

This commit prevents bad values being stored in the KeyMap
used by smf_jsatiles_region if they are present in the
initial mesh of tile numbers.  This prevents an error when
the values are subsequently fetched from the KeyMap
and passed to smf_jsatilei2xy.
smurf: Check for -ve tile coords before division

In smf_jsatilexy2i the x and y indices of the tile in the
all-sky map must be checked before dividing by the number
of pixels per side of a facet.  Otherwise small negative
numbers become zero upon integer division, and coordinates
within one facet below or to the left of the valid area
are not rejected, leading to the generation of spurious
tile indices.
smurf: Correct comment about tile region keymap