Fix assert failure when checking for infinite types

It was triggering on a certain combination of nested definitions.
Fix several piq/getopt parsing regressions introduced in v0.6.7

Specifically, "piqi getopt" and "piqi call" were no longer accepting some
unquoted literals as string arguments.

For example:

"1.2" was treated as a floating point number which resulted in "string
expected" error.

"1.2.3-rc1" was triggerring "invalid floating point literal" error.
Add --piq-relaxed-parsing option to "piqi pp" and "piqi check"

All commands that read Piq should be able to do so in relaxed mode. It used to
be only supported by "piqi convert".
piqi-0.6.10 release
Bump version number to 0.6.10-dev