Missing readline features when building with external libedit library

There are two issues related to external libedit reported for Fedora: https://bugzilla.redhat.com/show_bug.cgi?id=1187469 that non-ASCII characters don't work in interactive mode and https://bugzilla.redhat.com/show_bug.cgi?id=1180403 that backward search doesn't work.

The problem is that mysql binary uses just readline() function from libedit library and this function only offers basic functionality. So generally, the possible fix is either to use el_wgets() function from libedit and configure the backward search feature in mysql binary or fix libedit's readline function to offer this by default (of as another function).

Steps to Reproduce:
1. run mysql client that uses external libedit
2. copy & paste the following clauses in mysql client:
SELECT 'Chinese characters <汉字> are stripped';
3. '汉字' are stripped out in mysql client
4. press ctrl+R to activate background search in history

Actual results:

MariaDB [(none)]> SELECT 'Chinese characters <> are stripped';

+------------------------------------+

| Chinese characters <> are stripped |

+------------------------------------+

| Chinese characters <> are stripped |

+------------------------------------+

background search in history doesn't work

Expected results:

MariaDB [(none)]> SELECT 'Chinese characters <汉字> are stripped';

+------------------------------------------+

| Chinese characters <汉字> are stripped   |

+------------------------------------------+

| Chinese characters <汉字> are stripped   |

+------------------------------------------+

background search in history works

Reproducible for example with mariadb-10.0.17-1.fc21.