dependancy for spec files: if there is a pear_name defined calculate the provides accordingly

[tpokorra]

https://github.com/TBits/lbs-kolab/blob/Kolab_Winterfell/php-kolab-net-ldap3/php-kolab-net-ldap3.spec

%global pear_name Net_LDAP3

should tell us: provides: php-pear(Net_LDAP3)

so that roundcubemail depends on php-kolab-net-ldap3