Populate src.rpm header with dependencies early again

- BuildRequire checking requires a header populated with dependencies,
  commit a357c99c58a5e1367160dfa692f26d14bd3a3df1 changed this to
  occur too late for this purpose. Move to initSourceHeader() seems
  to fix, also goes to show we dont have a test-case for buildrequires...
Add a simple testcase for buildrequires functionality
Oh yes, its Monday alright...

- Two typos in previous commit, I fail to see how I managed to test
  this as "working"
Populate manual dependencies into spec pkg headers early too

- Similar to commit 1b41c91431d37295701281ff208f99a51f660c89, rpmspec
  and other tools expect to find manually specified dependencies
  from the headers of a freshly parsed spec. This means we need to
  add this cruft two times: once for the manual dependencies and then
  scratch all that and redo from start after automatic dependencies
  have been discovered at the end of package build.
- Fixes another regression (rpmspec dependency queries went dead)
  introduced in commit a357c99c58a5e1367160dfa692f26d14bd3a3df1
Add a simple testcase for rpmspec queries
Use fingerprinting in rpmal file matching

The code in rpmdb already supports fingerprinting, which led to
file dependency problems being reported against installed packages,
but ignored for against new packages.

The use of the fingerprinting code does not seem to make the
dependency check slower in my tests.
Use fingerprinting in checkInstDeps

We already do fingerprinting in rpmal and rpmdb, but we missing
installed file dependencies. Fortunately we can make use of the
conflict and require caches to find potential candidates.
Simplify rpmcliTransaction code a bit
Add lost fpLookupEquals() call in depends.c

Lost in copy and pasting. Does not make much difference,
except that the code should be faster with the check.
Delete trigger indexes too from header before adding again (RhBug:1131892)

- Fixes regression introduced in the regression-fix
  commit 0bda2faa4de368a87f85084856a5fed701774acb, *facepalm*
- Unlike other dependency types, trigger dependencies involve a fourth
  tag which we forgot to delete before adding again, causing duplicate
  trigger indexes
Rename confcache to confilecache and reqcache to reqfilecache

No functional changes.
Check for reqfilecache existance before iterating over the filelist

Improves the symmetry between install and erase element checking ;)