demo: Use allocation for model string.
sr_driver_scan: Enforce options passed in by client.
bindings: Re-enable Java, but ignore create_analog_packet().

This will need some fixing.
bindings: Fix out-of-tree build.

This closes #473.
Refactor scan options check.
Check the version of the AX_CXX_COMPILE_STDCXX_11 macro.
autogen.sh: Also warn if AX_CXX_COMPILE_STDCXX_11 is not available.

This fixes an error message when the file is not installed at all:

  ./autogen.sh: 67: [: Illegal number:

Turn the AX_CXX_COMPILE_STDCXX_11 errors into warnings though, since
it is (and should be) possible to build libsigrok (just the C library)
just fine, even without that macro or with an older version of it.
Add a sr_analog_init() API to initialize sr_datafeed_analog2 struct.

It fills the fields with the reasonable default values that should suits
most of the drivers.
Drivers are obviously free to override the fields they want after
initializing.

This fixes bug #476.