Updates to rpm/libstrophe.spec

To build the profanity IM client, I had to make a proper `-devel` package for strophe. In the process, I also explicitly listed out the requirements. Without them, I received the following while building on Fedora 19:

```
[kwhite@li356-23 ~]$ rpmbuild -bb ~/rpmbuild/SPECS/libstrophe.spec
Executing(%prep): /bin/sh -e /var/tmp/rpm-tmp.VccYgW
+ umask 022
+ cd /home/kwhite/rpmbuild/BUILD
+ cd /home/kwhite/rpmbuild/BUILD
+ rm -rf libstrophe
+ /usr/bin/gzip -dc /home/kwhite/rpmbuild/SOURCES/libstrophe_git.tar.gz
+ /usr/bin/tar -xvvf -
drwxrwxr-x kwhite/kwhite     0 2013-11-18 17:25 libstrophe/
drwxrwxr-x kwhite/kwhite     0 2013-11-18 17:25 libstrophe/src/
# ....
+ STATUS=0
+ '[' 0 -ne 0 ']'
+ cd libstrophe
+ /usr/bin/chmod -Rf a+rX,u+w,g-w,o-w .
+ ./bootstrap.sh
./bootstrap.sh: line 8: aclocal: command not found
./bootstrap.sh: line 9: automake: command not found
./bootstrap.sh: line 10: autoconf: command not found
error: Bad exit status from /var/tmp/rpm-tmp.VccYgW (%prep)


RPM build errors:
    Bad exit status from /var/tmp/rpm-tmp.VccYgW (%prep)
```