Update to lzip version 1.18 which includes the following changes:

• New options -a and --trailing-error.
• Decompression time has been reduced by 2%.
• Removed decompression support for version 0 files.
• Some bug fixes.
• New chapter 'Trailing data' in the texinfo documentation.

Plus the following changes from version 1.17, which we missed:

• New chapter 'Quality assurance' in the texinfo documentation.
• Reorganization of the compression code.