Changed processing unique constraint name.

Mr. Devananda found that dollar sign can be used as special symbol in
various programming langugages and proposed to use `0` instead of `$`.
So unique constraint name convention was changed from "uniq_t$c1$c2$c3"
to "uniq_t0c10c20c3" where `0` it is delimiter, `t` it is table name and
columns `c1`, `c2`, `c3` are in UniqueConstraint.

Function `_raise_if_duplicate_entry_error()` modified respectively to
new unique constraint name convention.

Change-Id: I88208dc03b55bbbc709b18580048c008004c9fda
Merge "Changed processing unique constraint name."