[raster] ST_Band that takes delimeter doesn't accept all characters

[robe]

As noted in #2180 we should deprecate this function or fix it to be less restrictive.

In revising the docs, I discoveed I can not do this:

ST_Band(rast,'1|2|3', '|')

Which is my next favorite delimeter next to the default ','. The reason is because the function is defined like this:

SELECT st_band($1, regexp_split_to_array(regexp_replace($2, '[[:space:]]', '', 'g'), $3)::int[]) 

So use of any kind of white space or regular expression key character is disallowed. We should clean this up a bit or just deprecate this function.

As stated why anyone would want to change the delimeter seems spurious and having an additonal function just so I can type '1,2,3' instead of the slightly longer

'{1,2,3}'::int[]
}} I don't think is worth it.