replace all unbundled section references with symbols

Currently we're checking for several special cases when deciding whether
to convert unbundled section references to their corresponding symbol
references.  We do it for all unbundled text sections as well as three
specific data sections.

There's no reason I can think of for why we shouldn't just do it for
_all_ unbundled sections.
Merge pull request #427 from jpoimboe/replace-unbundled-references

replace all unbundled section references with symbols