Introspection for builtin functions

[SimonKing]

Up to now, the attempt to inspect Python builtins with ? results in a TypeError, raised by Python's inspect module. This is when the argspec or the source file is requested.

I suggest to return generic information. With the attached branch, we get

sage: range?
Docstring:
range(stop) -> list of integers range(start, stop[, step]) -> list of
integers

Return a list containing an arithmetic progression of integers.
range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
When step is given, it specifies the increment (or decrement). For
example, range(4) returns [0, 1, 2, 3].  The end point is omitted!
These are exactly the valid indices for a list of 4 elements.
Init docstring: x.__init__(...) initializes x; see help(type(x)) for signature
File:           
Type:           builtin_function_or_method

[SimonKing]

New commits:

​30543e7	Avoid source inspection for cached cython methods without arguments
​a0b829d	Make a cached function/method work with default argspec when introspection fails
​831173b	Merge branch 't/17814/make_calling_a_cached_method_independent_of_source_code_inspection' into t/17814/rebased-make_calling_a_cached_method_independent_of_source_code_inspection
​b340eeb	Use embedded signature for introspection
​0e8ef00	Catch syntax error when extraction of signature fails
​dffa765	Introspection of builtins returns generic data instead of raising an error

[vbraun]

Merge conflict, can you merge in 6.7.beta3

Code looks good, set to positive review when you are done.

[SimonKing]

Can someone else please do the merge, I will be too busy till next week.

[jdemeyer]

New commits:

​e478d5b

Merge tag '6.7.beta3' into t/18249/introspection_for_builtin_functions