Missing optional dependencies:

[nijel]

The detectPow function at:
https://github.com/phpmyadmin/phpmyadmin/blob/master/libraries/Util.php#L38
will use bcpow or gmp_pow or pow functions, the bcpow & gmp_pow functions require:
php5-bcmath
php5-gmp
packages

fix:
1. in docker, add php5-bcmath:
https://github.com/phpmyadmin/docker/blob/master/Dockerfile#L4
2. in debian, add under "Recommends" a PHP bcmath package:
https://sources.debian.net/src/phpmyadmin/4:4.6.4%2Bdfsg1-1/debian/control/?hl=29#L29

Reported by Emanuel Bronshtein.

[nijel]

I've looked at all Util::pow use cases and I don't think we're having any benefit when using bcmath or gmp functions here, so adding this dependency has IMHO no reason.

See also phpmyadmin/phpmyadmin#12595, where I propose to remove this code altogether.

[nijel]

Code has been removed, so there is no need for these dependencies.