Clarify wording of log message when err is cleared.

Re http://stackoverflow.com/questions/18983601/why-is-there-a-0-cleared-by-call-to-connect-method-warning-in-dbi-trace
Stop setting err to 0 when creating a new drh
Fix RT#83132 - move DBIstcf* constants to utils export group
Clarification of ReadOnly attribute when driver cannot enforce it
ignore a load of generated files in .gitignore

On Windows, a load of files get generated which the .gitignore does not
ignore
Sorted .gitignore, added test_output_* and MYMETA.*. Added .gdbinit
Fix POD for SQL_BIGINT type constant

It's exported as of DBI-1.54, with the ODBC value.
Merge pull request #5 from ilmari/fix-bigint-pod

Fix POD for SQL_BIGINT type constant
Added Changes for PR5 and polished wordings
Add perl 5.18 to .travis.yml
Added ErrChangeCount attr to fix PrintWarn for STROE etc. RT#89015.
No longer show quote and quote_identifier calls at trace level 1.
Enable PrintWarn by default. (Trial for testing by developers.)
Prep for 1.628_50 trial release.
Replaced ErrChangeCount with alternative approach that's binary compatible.

This reverts most of 70fe6bd7.
Fix err_hash for threaded perl
Tidy Changes notes
Switch to a modern form of handling $VERSION & $XS_VERSION

Per http://www.dagolden.com/index.php/369/version-numbers-should-be-boring/#comment-673
and https://rt.cpan.org/Public/Bug/Display.html?id=89618
Prep for 1.629_50 release
Changed DBD::Gofer ping while disconnected set_err from warn to info.