Sorry to dig up this old thread, but I think it is rather important to give some instructions as I too was stuck until I just learnt how to apply patches.
.patch files are processed, on linux, by the patch command.
To patch roundcube, you need to use your SSH access and make sure you have permission to run this (I used root):
Upload the patch file to your server and then move it to the directory where your roundcube is installed.
cd (change directory) to the directory where your roundcube is installed.
Then, run the patch command:
patch -p0 <0.1-beta2.2.patch
The output should then be if all is well:
patching file program/steps/mail/func.inc
So, my entire process (for me!) was:
scp the patch file to my root directory from my PC (or using winSCP on Windows):
scp ~/Desktop/0.1-beta2.2.patch [email]root@ahem.com[/email]:/root/
SSH in to my server as root.
Move the file from my root directory to my roundcube directory.
root@ahem.com [~]# mv 0.1-beta2.2.patch /usr/local/cpanel/base/roundcube
cd to where my roundcube is installed:
root@ahem.com [~]# cd /usr/local/cpanel/base/roundcube
run the patch:
root@ahem.co [/usr/local/cpanel/base/roundcube]# patch -p0 <0.1-beta2.2.patch
patching file program/steps/mail/func.inc
Job done!