Treat all externally loaded modules as embedded

This fixes the actual problem in piqi-ocaml when the runtime was trying to
locate imported modules in the filesystem during initialization.
Fix a problem with loading imports from extended modules
Small code improvement
Fix: finite types incorrectly reported as infinite (refix #39)
Add tests for infinite type detection
piqi compile: add new experimental -f and -t piqi command-line options
Minor piqilib API improvements
Move custom-field property from piqi-lang to piqi-spec
Rename --leave-tmp-files to --keep-tmp-files
Fix: make conversion to piq string follow piq_frameless_output setting

This was affecting serialization runtime ("piqi server" and piqilib/OCaml).
Internal improvements
More internal improvements
Fix distclean target
Merge pull request #44 from yfyf/fix_distclean

Fix distclean target
Add Ignas Vyšniauskas to THANKS
Add support for cross-compiling win32 executable on Linux
Merge remote-tracking branch 'upstream/master'
Bringing piqi in sync with alavrik/piqi