PATCH: some extra options in Image Magick completion

[Oliver Kiddle <okiddle@xxxxxxxxxxx>]

At some point when using Image Magick's convert command I added a couple
of missing options to the completion in my local branch. But the
function is missing many other options and needs rather more work than
just this so they've sat in my branch for some time. Rather than have it
go to waste, here's the patch.

Oliver

diff --git a/Completion/Unix/Command/_imagemagick b/Completion/Unix/Command/_imagemagick
index 3afa108ae..b7671fe49 100644
--- a/Completion/Unix/Command/_imagemagick
+++ b/Completion/Unix/Command/_imagemagick
@@ -262,7 +262,10 @@ case "$service" in
     _arguments -C -M 'm:{a-z}={A-Z}' \
       '-adjoin[join images]' \
       '-affine[drawing transform matrix]:matrix' \
+      '-alpha[set the alpha channel]:alpha' \
       '-antialias[remove pixel aliasing]' \
+      '-authenticate[decrypt image with specified password]:password' \
+      '-attenuate[lessen (or intensify) when adding noise to an image]:value' \
       '-append[append image sequence]' \
       '-average[average image sequence]' \
       '-background[specify background color]:color:_x_color' \
@@ -301,6 +304,7 @@ case "$service" in
       '(-endian)+endian' \
       '-enhance[enhance image]' \
       '-equalize[histogram equalization]' \
+      '-features[analyze image features (e.g. contrast, correlation)]:distance' \
       '-fill[specify color to use when filling a graphic primitive]:color:_x_color' \
       '-filter:filter type for resizing:(Point Box Triangle Hermite Hanning Hamming Blackman Gaussian Quadratic Cubic Catrom Mitchell Lanczos Bessel Sinc)' \
       '-flatten[flatten a sequence of images]' \
@@ -315,12 +319,14 @@ case "$service" in
       '-gravity:image gravity:(Center North NorthEast East SouthEast South SouthWest West NorthWest)' \
       '-implode:implosion factor (0.0 - 99.9%%)' \
       '-interlace:interlacing scheme:(None Line Plane Partition)' \
+      '-interpolative-resize[resize image using point sampled interpolation]:geometry' \
       '-label:label string' \
       '-layer:layer type:(Red Green Blue Matte)' \
       '-linewidth:line width' \
       '-loop:number of iterations (GIF animation)' \
       '-map[single image colormap file]:picture file for colors:_imagemagick' \
       '+map[all images colormap file]:picture file for colors:_imagemagick' \
+      '-mask[associate a mask with the image]:file:_files' \
       '-matte[store matte channel]' \
       '-modulate:<brightness>,<saturation>,<hue>' \
       '-monochrome[transform to black and white]' \
@@ -352,6 +358,7 @@ case "$service" in
       '-size:image size (<width>x<height>+<offset>)' \
       '-solarize:solarization threshold' \
       '-spread:neighborhood size' \
+      '-support[specify resize support]:support (>1.0 is blurry, < 1.0 is sharp)' \
       '-swirl:swirl tightness' \
       '-texture:background texture image:_imagemagick' \
       '-threshold:threshold for maximum intensity' \