Increase number of post-meta keys to 30 and sort them

[alexkingorg]

I've found that the post-meta drop down list is hard to use in 2 ways:

1. I have ~15 keys and keys disappear from the list and I have to look them up
2. Since keys are not always in the list and can appear in a different order each time, it is hard to find a key with visual scanning even if the key *is* in the list.

This patch increases the key list from 10 to 30, and sorts the keys.

If this is rejected, please e-mail me to let me know and I'll write an auto-complete plugin instead.

[alexkingorg]

patch

[markjaquith]

I like this. It'll only matter for people who have more than 10 keys, and those people probably want to see them for easier access.

30 is a reasonable number. I can also implement the filter suggestion from #1865 , so people can easily change it.

See patch.

[markjaquith]

Move limit to 30, add filter, natcasesort()

[markjaquith]

Matt, Ryan, others -- any objections to my patch?

[matt]

This is fine.

[markjaquith]

(In [4413]) increase postmeta dropdown limit to 30, add filter for the limit, sort the keys. props Alex King. fixes #3237