"I" is case-sensitive when setting gender

Currently, it's case-insensitive when determining whether to allow the change, but case-sensitive when determining the target, leading to this:

```
< yazdmich> bucket: what gender am i?
< Bucket> yazdmich: Grammatically, I refer to you as androgynous.  See http://wiki.xkcd.com/irc/Bucket#Docs for information on setting this.
< yazdmich> bucket: i am male
< Bucket> Okay, yazdmich
< yazdmich> bucket: what gender am i?
< Bucket> yazdmich: Grammatically, I refer to you as androgynous.  See http://wiki.xkcd.com/irc/Bucket#Docs for information on setting this.
<@Shrdlu> Bucket: what gender is i
< Bucket> Shrdlu: i is male.
```