Update README.md

Added two modifications to make the descriptions more clear.
Revert "Remove signal DoubleSpendDetected, use function"

This reverts commit 0da6b3fd187da3aa810aaa584d8bd197ad4fa2b9.
Revert "Check signatures before respend relay"

This reverts commit 88dd3598d22197a22565e524cecdc08107cf76ac.
Revert "Formatting, spelling, comment fixes."

This reverts commit 7a19efe04069d9a1e251cdc94b25184f76d9d901.
Revert "Add release notes entry"

This reverts commit 9fa53dd3bdc6f62b16a7c2b970449c8c35f4c41b.
Revert "Add -respendnotify option and new RPC data"

This reverts commit 9004798e62e987ddf50030b17fa1881b63dd5e45.
Revert "UI to alert of respend attempt affecting wallet."

This reverts commit ada5a067c75f19a724cc054286ecf2254e5dbe8f.

Conflicts:
	src/qt/guiconstants.h
	src/wallet.h
Revert "Relay double-spends, subject to anti-DOS"

This reverts commit d640a3ceab4f4372c2a0f738c1286cfde4b41b50.
Revert "CBloomFilter::clear() method"

This reverts commit 8fbf03995df9a2003be603be1a930bc3373d56e0.
Merge pull request #4558

8f3f94a Revert "CBloomFilter::clear() method" (Wladimir J. van der Laan)
98e84aa Revert "Relay double-spends, subject to anti-DOS" (Wladimir J. van der Laan)
3015e0b Revert "UI to alert of respend attempt affecting wallet." (Wladimir J. van der Laan)
39d3f2c Revert "Add -respendnotify option and new RPC data" (Wladimir J. van der Laan)
680f725 Revert "Add release notes entry" (Wladimir J. van der Laan)
ad26dc9 Revert "Formatting, spelling, comment fixes." (Wladimir J. van der Laan)
cd057bf Revert "Check signatures before respend relay" (Wladimir J. van der Laan)
67cc8f2 Revert "Remove signal DoubleSpendDetected, use function" (Wladimir J. van der Laan)
Merge pull request #4557

92b8587 Update README.md (elkingtowa)
Harmonize importprivkey and importaddress documentation
build: fix broken boost chrono check on some platforms

If clock_gettime is implemented outside of libc (librt in this case), configure
would fail when testing boost. Since clock_gettime is not present on all OSs,
boost only uses it when it can. Check for it in librt and add it to LIBS if
found, but don't fail if it's not (since boost won't be expecting it in this
case).

Also, reverse the link order as necessary for static libs.

Note that it's possible that there are other similar cases for boost, which may
be handled the same way.
gitian: remove unneeded option after last commit
Merge pull request #4571

a7ec027 gitian: remove unneeded option after last commit (Cory Fields)
460b32d build: fix broken boost chrono check on some platforms (Cory Fields)