Description:
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The function "dba_insert" doesn't work as expected with most handlers.
On calling "dba_insert" on an already existing key the function should return false and do not trigger a warning but that's not the case on most tested handlers.

Test script:
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$dba = dba_open(sys_get_temp_dir() . DIRECTORY_SEPARATOR . uniqid('dba_'), 'c', 'qdbm');

var_dump(dba_insert('key', 'test1', $dba));
var_dump(dba_insert('key', 'test2', $dba));
var_dump(dba_fetch('key', $dba));

Expected result:
----------------
bool(true)
bool(false)
string(5) "test1"

Actual result:
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           RETURN1  RETURN2  WRANING	
flatfile   true     false    YES
inifile    true     true     NO
gdbm       true     false    YES
qdbm       true     false    YES
db4        true     false    NO
-> Didn't test not listed handlers !