Allow separate repository DDL generation

Nuxeo can now start with a new nuxeo.vcs.ddlmode parameter that specifies how the DDL for repository initialization should be executed at startup. Depending on the chosen mode, the DDL to be executed may not be executed at all and instead dumped to the file log/ddl-vcs-default.sql. The possible values for nuxeo.vcs.ddlmode are:

• ignore: no DDL detected or executed; replaces nuxeo.vcs.noddl=true
• compat: compatibility mode with previous version, always executes DDL that recreates stored procedures (and does not attempt to detect existing ones); replaces nuxeo.vcs.noddl=false
• execute: executes the DDL and starts Nuxeo normally.
• dump: dump the DDL (if any) to the file but still executes it and starts Nuxeo normally.
• dump,ignore: dump the DDL (if any) to the file but does not execute it and starts Nuxeo normally (will likely result in errors).
• dump,abort: dumps the DDL (if any) to the file, and if not empty aborts startup.

For Nuxeo 6.0 and Nuxeo 7.10 the default is nuxeo.vcs.ddlmode=compat. For Nuxeo 8.1 the default will be nuxeo.vcs.ddlmode=execute.

Note that all this applies to the DDL for the document repository, but not DDL used by other users of SQL in the platform (directories, quartz, JPA persistence).