DDL sql execution error when upgrading from 1.9.10+ to 2.0.1+

Before upgrading my production moodle site to version 2, I am practising the upgrade process on another server from 1.9.10+ to 2.0.1+

Here's what I have done:

1) made a duplicate of the 1.9 moodledata directory
2) made a duplicate of the 1.9 MySQL database, and made a new user with appropriate privileges
3) downloaded mooodle version 2 via CVS, and did NOT copy over the original config.php file, nor did I copy over any non-standard mods, blocks or themes or anything else.
4) accessed the top page of this install via Firefox
5) as expected, the install window loads, and I type in the relevant details (paths to Moodledata, db name, user name etc.)
5) then, as expected the "Your Moodle files have been changed..." warning appears in browser window (.../admin/index.php)
6) clicked on Continue, and the "Server checks" reports no issues (Your server environment meets all minimum requirements) other than recommendation to install php Intl extension. Note: I have successfully carried out completely fresh installs of version 2 without the intl extension.
8) clicked on Continue, and the "Plugins check" informs me that I have various Non-standard blocks and Modules (i.e. the tables for these non-standard items exist in the database). However, according to this doc
http://docs.moodle.org/en/Upgrading_to_Moodle_2.0#A_word_about_optional_plugins_and_themes
these non-standard mods and blocks should not be a problem. Apparently their corresponding tables will be left dormant until I install updated versions of the mods and blocks.
9) clicked on Upgrade, course files and blog attachments are migrated, and then I get the following error message (see also attached GIF):

DDL sql execution error

Debug info: MySQL server has gone away
ALTER TABLE mdl_log MODIFY COLUMN ip VARCHAR(45) NOT NULL DEFAULT '' after userid
Stack trace:

• line 397 of /lib/dml/moodle_database.php: ddl_change_structure_exception thrown
• line 636 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
• line 88 of /lib/ddl/database_manager.php: call to mysqli_native_moodle_database->change_database_structure()
• line 75 of /lib/ddl/database_manager.php: call to database_manager->execute_sql()
• line 636 of /lib/ddl/database_manager.php: call to database_manager->execute_sql_arr()
• line 648 of /lib/ddl/database_manager.php: call to database_manager->change_field_type()
• line 1042 of /lib/db/upgrade.php: call to database_manager->change_field_precision()
• line 1360 of /lib/upgradelib.php: call to xmldb_main_upgrade()
• line 252 of /admin/index.php: call to upgrade_core()

Fatal error: Exception thrown without a stack frame in Unknown on line 0

10) there is a Continue button, which when I click takes me back to the "Your Moodle files have been changed, and you are about to automatically upgrade your server to this version:". On trying to re-run the process I am taken back to the same error.

Hope this information helps to fix this problem.

I see that "DDL sql execution error upon 1.9 to 2.0 migration" has been reported: MDL-22503.
I have also posted a question re this error: http://moodle.org/mod/forum/discuss.php?d=167997