Added find() & get() to environment (closes #326)

[coatless]

Modified load order of Rcpp.h to allow for symbol object to be used within Environment.h by placing Symbol.h before Environment.h

Used the .c_str() on symbol to ensure exception call could be made. (Assuming the symbol name is not NULL).

Fixed a space in changelog

[coatless]

The Travis-CI check being green is a bit misleading as the travis-log contains:

* checking foreign function calls ... NOTE
Registration problem:
  symbol ‘symbol’ in the local frame:
   .Call(symbol)
See chapter ‘System and foreign language interfaces’ in the ‘Writing R
Extensions’ manual.

My local check on Rcpp does not have this error listed.

* checking foreign function calls ... OK

[eddelbuettel]

We have been getting that warning for a long time; it is grandfathered as "technically correct" (we do make that call, but it is Rcpp internals and needed for some functionality). I guess it depends if you call with --as-cran and/or which checking variables you have set. We can discuss off-line, or I just email you my ~/.R/check.environ.

...
* checking replacement functions ... OK
* checking foreign function calls ... NOTE
Registration problem:
  symbol ‘symbol’ in the local frame:
   .Call(symbol)
See chapter ‘System and foreign language interfaces’ in the ‘Writing R Extensions’ manual.
* checking R code for possible problems ... OK
* checking Rd files ... OK
...

[eddelbuettel]

Looks like a nice PR. As it re-orders headers I'll be prudent and run a rev.dep check just in case.

[kevinushey]

LGTM as well, modulo the check to ensure re-ordered headers aren't an issue.

[eddelbuettel]

Looks like it passed the reverse depends with flying colors.

[coatless]

The Registration problem seems to be triggered by:

Rcpp/R/Module.R

Line 199 in 0dd0fb6

xp <- .Call( symbol )

I think there is a way to actually suppress / remove the warning.