Misc fixes and improvements for Requires and Requires.private

[Loïc Minier]

        Hi there

 Could you please consider merging this branch?
 http://bzr.debian.org/bzr/users/lool/pkg-config

196: Explain Libs.private versus Requires.private
195: Fix typo in man page and improve Requires.private section
194: Document --cflags-only-I in the man page
193: Allow for missing Requires in some cases
192: Add a test for missing Requires (failing)
191: Add an ignore_requires_private defaulting to TRUE
190: Cleanup logic when ignoring Requires
189: Check for missing .pc and Requires.private (failing)
188: Record pkg-config's output with LC_ALL=C set
187: Allow testing for error exit codes and output
186: Add .bzrignore

    Thanks!
-- 
Loïc Minier