2d suitability() is inconsistent with newCursor() in certain nested field cases

Geo2dType::suitability() uses getFieldsDotted() to extract a geo field from a query. I don't believe this is correct, because getFieldsDotted() recursively extracts fields from nested objects, and query fields use dotted top level and not nested fields.

Eg to query field 'a.b' you would write a query

not { a:

}. The latter is an equality predicate on 'a' not on 'a.b'.

Geo2dType::newCursor() looks for a geo index field name in a query without expanding nested document field names (I believe correctly).

This appears to cause a problem in cases where suitability() is inconsistent with newCursor() - suitability() says the index is not useless, but newCursor() asserts when trying to create a cursor on the index.

We should also check the s2 code to see if the same issue is present there.

Test

c = db.c;

c.drop();

c.save( { a:{ loc:[ 0, 0 ], b:5 } } );

// Count works as expected without an index.                                    

assert.eq( 0, c.count( { a:{ loc:[ 0, 0 ] } } ) );

c.ensureIndex( { 'a.loc':'2d' } );

// Count asserts with a 2d index.                                               

assert.eq( 0, c.count( { a:{ loc:[ 0, 0 ] } } ) );

Error

Sun Feb 24 18:03:00.854 JavaScript execution failed: count failed: {

	"errmsg" : "exception: missing geo field (a.loc) in : { a: { loc: [ 0.0, 0.0 ] } }",

	"code" : 13042,

	"ok" : 0

} at src/mongo/shell/query.js:L180