added option to set PKCS#12 alias name

[jdelker]

This change adds a new option "usealias" to the export-p12 command.
If set, it uses the $short_name as a friendly name for the certificate.

Motivation:
The friendly name aka alias of the certificate/key pair stored in the PKCS#12 container is often used by other software to uniqly select a particular entry. So far, any PKCS#12 container created by EasyRSA was simply unusable by such software.

This probably replaces #45.

[TinCanTech]

@jdelker Thank you, this looks good.

This probably replaces #45.

Agreed. Although #45 was right at the top of my list before #544 ;-)

There is only one doubt: Is usealias the right command option ?

Here's options:

• fname
• use-fname
• friendly
• use-friendly
• use-friendly-name
• usefn (I like this one)

You even describe the option as:

use <filename_base> as friendly name

[jdelker]

@TinCanTech

There is only one doubt: Is usealias the right command option ?

I actually changed this back and forth, but haven't really been satisfied with any of them ;)
So any other would do also.
I go along with usefn just fine.